While Enchanting buffs can be purchased, most of the Engineering gizmos will require you have have the appropriate level of Engineering to use. So for the dedicated PVPer, Engineering is just about required for one of your two primary professions.
Let's take a look at some of the Engineering gadgets you can use in PVP, and some strategies to help you excel with the help of Engineering.
Large Copper Bomb
Requires Engineering (105)
Use: Inflicts 43 to 57 Fire damage and stuns targets in a 5 yard radius for 1 sec. Any damage will break the effect. Unreliable against targets higher than level 36.
Cooldown: 1 min
1 sec cast
This is the first (or lowest level) bomb that's worth using in PVP. Usually you'll level Engineering past this. But imagine using this to stop a flag runner or stun attackers on you and allow you to get away.

Small Bronze Bomb
Requires Engineering (120)
Use: Inflicts 73 to 97 Fire damage and stuns targets in a 3 yard radius for 2 sec. Any damage will break the effect. Unreliable against targets higher than level 39.
Cooldown: 1 min
1 sec cast
Use this the same way as you'll use all bombs; to stop someone you want to catch, or to freeze a chaser to let you get away.
Flying Tiger Goggles
Binds when equipped
Head Cloth
27 Armor
+4 Stamina
+4 Spirit
Durability 35 / 35
Requires Engineering (100)
These are not the best twink goggles, but these are a step in that direction. Until you get to the Green Tinted Goggles, these are the best head gear for level 19 twinks.
Big Bronze Bomb
Requires Engineering (140)
Use: Inflicts 85 to 115 Fire damage and stuns targets in a 5 yard radius for 2 sec. Any damage will break the effect. Unreliable against targets higher than level 44.
Cooldown: 1 min
1 sec cast
Use this the same way you'll use all the bombs Engineering can make. Note that the stun effect is of more value than the damage. Unless you managed to get it off against a group of non-twinks. If you could use this drop a group of low health level 12s in WSG, you would have seen Heaven.
Minor Recombobulator
Trinket
Requires Engineering (140)
Use: Dispels Polymorph effects on a friendly target. Also restores 150 to 250 health and mana.
Cooldown: 5 min
Charges: 10 (Expendable)
This is the first and only trinket (until you grind up to the Alliance or Horde trinket, which will take hundreds of WSG runs) a level 19 can use. Combine this with a health potion (which is on a different timer) and you can shrug off lots of damage.

Explosive Sheep
Requires Engineering (150)
Use: Summons an Explosive Sheep which will charge at a nearby enemy and explode for 135 to 165 damage. Lasts for 3 min or until it explodes.
Cooldown: 1 min
This may not have the best PVP value ever, but it is lots of fun to see a sheep charging at your enemies. It equals a whole other attack, and some users claim that it attacks stealthed enemies, and does area damage.
Green Tinted Goggles
Binds when equipped
Head Cloth
35 Armor
+8 Stamina
+7 Spirit
Requires Engineering (150)
This is the best head gear for the 10-19 PVP bracket. You can put a +100 health Lesser Arcanum of Constitution on it to make it a truly twinked out piece of gear.
Iron Grenade
Requires Engineering (175)
Use: Inflicts 132 to 218 Fire damage and stuns targets for 3 sec in a 3 yard radius. Any damage will break the effect. Unreliable against targets higher than level 50.
Cooldown: 1 min
1 sec cast
The main difference between grenades and bombs: you can use grenades while running! Throw one of these at someone chasing you without having to stop running. (You will have to learn the trick of aiming them with a one-second lag to detonation.) Now you're getting into “must-have” territory for the true PVPer.
Discombobulator Ray
Use: Transforms the target into a Leper Gnome, reducing its melee and spell damage by 40 and its movement rate by 20% for 12 sec.
Cooldown: 1 min
Charges: 5 (Expendable)
This ray is pure PVP goodness. Look at all the wonderful things it does; slows the target, humiliates him or her by turning them into a gnome leper, and reduces both their spell and their melee damage.
This is instant cast, you don't have to equip it, and the cool down is only one minute. For fun and effective PVP, you can't ask for more!
Gnomish Shrink Ray
Binds when equipped
Trinket

Requires Engineering (205)
Use: Shrinks the target reducing their attack power by 250. That's what it usually does anyway.
Cooldown: 5 min
You have to be an Gnomish Engineer to make this. It's a gamble to use it, it has unpredictable effects. However, for having lots of fun, and with the possibility to pwn someone in a humiliating manner, you can't beat this gadget.
Goblin Bomb Dispenser
Binds when picked up
Trinket
Requires Engineering (230)
Use: Creates a mobile bomb that charges the nearest enemy and explodes for 315 to 385 fire damage.
Cooldown: 30 min
This bomb does area effect damage and chases down enemies in agro range. Great for casting when your enemies are clumped up, and you don't want to get too close. As the name says, its for Goblin Engineers.
Gnomish Goggles
Binds when picked up
Head Cloth
45 Armor
+9 Agility
+9 Stamina
+9 Spirit
Requires Engineering (210)
Gnomish Engineers can make this headgear, which, depending on your level, can be better than quest or dropped gear.
Gnomish Net-o-Matic Projector
Binds when equipped
Trinket
Requires Engineering (210)
Use: Captures the target in a net for 10 sec. The net has a lot of hooks however and sometimes gets caught in the user's clothing when fired.
Cooldown: 10 min
This gadget is a great way to stop a flag runner, or capture someone that's trying to get away. It can backfire and net you. It's an instant cast trinket, and can be a lot of fun.
The Big One
Requires Engineering (225)
Use: Inflicts 340 to 460 Fire damage and stuns targets for 5 sec in a 10 yard radius. Any damage will break the effect. Unreliable against targets higher than level 60.
Cooldown: 1 min
3 sec cast

This great bomb has a huge radius for area of effect. That's balanced by the three second casting time.
Gnomish Mind Control Cap
Binds when equipped
Head Cloth
50 Armor
+14 Spirit
Durability 45 / 45
Requires Engineering (215)
Use: Engage in mental combat with a humanoid target to try and control their mind. If all works well, you will control the mind of the target for 20 sec. Increased chance of failure when used against targets over level 60.
Cooldown: 30 min
This can freak people out. If if works, they become your pet, and you can sick them on members of their own faction.
Gnomish Death Ray
Binds when picked up
Trinket
Use: The device charges over time using your life force and then directs a burst of energy at your opponent.
"Death or Serious Injury may result from use of this device."
Cooldown: 5 min
Charge it up and let it rip. Amazing amounts of one-shot damage result. Suppose a frost Mage has frozen you, or a Hunter has you in a wing clip. Pull up and blast with this weapon. You'll kill them, or do serious damage.
Green Lens
Binds when equipped
Head Cloth
57 Armor
+10 Stamina
<Random enchantment>
Durability 50 / 50
Requires Engineering (245)
There's no telling what the <Random Enchantment> will be when you make one of these. You could get lucky and make something that matches you're needs exactly (for example, Green Lens of Fiery Wrath: 10 stamina and 34 fire damage.)
Or, it could be something you don't need at all.
Thorium Grenade
Requires Engineering (260)

Use: Inflicts 300 to 500 Fire damage and stuns targets for 3 sec in a 3 yard radius. Any damage will break the effect. Unreliable against targets higher than level 67.
Cooldown: 1 min
1 sec cast
A higher level grenade with more damage and a three second stun.
Major Recombobulator
Trinket
Requires Engineering (275)
Use: Dispels Polymorph effects on a friendly target. Also restores 375 to 625 health and mana.
Cooldown: 5 min
This trinket is a great way to stack healing on yourself with potions.
Spellpower Goggles Xtreme Plus
Binds when equipped
Head Cloth
57 Armor
Durability 45 / 45
Requires Engineering (270)
Equip: Increases damage and healing done by magical spells and effects by up to 27.
Depending on your level, these goggles can be the best head gear you can find.
Arcane Bomb
Requires Engineering (300)
Use: Drains 675 to 1125 mana from those in the blast radius and does 50% of the mana drained in damage to the target. Also Silences targets in the blast for 5 sec.
Cooldown: 1 min
Charges: 1 (Expendable)
1.5 sec cast
This is terribly expensive. Oh, but the sheer joy of silencing, damaging casters, and draining their mana all at the same time. Used wisely, this bomb can turn the tide of a big battle. Note that this also affects any casters on your side in the blast radius. So, as stated; use it wisely!
Imagine horde (or alliance) coming across the Alterac Valley bridge in a huge clump. Drop one of these and the casters are gimped.
Adamantite Grenade
Requires Engineering (325)
Use: Inflicts 450 to 750 Fire damage and stuns targets for 3 sec in a 3 yard radius. Any damage will break the effect. Unreliable against targets higher than level 80.
Cooldown: 1 min
1 sec cast
Another grenade upgrade.

Frost Grenade
Requires Engineering (325)
Use: Blasts enemies for 75 to 125 Frost damage and freezes them in place for up to 5 sec. Damage caused may interrupt the effect.
Cooldown: 1 min
1 sec cast
This has a five second freeze. That five seconds allows you to do all kinds of things: drink a potion, get behind them to attack their back, run away, freeze a flag runner, and so on.
Cogspinner Goggles
Binds when equipped
Head Leather
<Random Enchant>
220 Armor
Durability 60 / 60
Requires Engineering (340)
You might hit a home run when you make these and get a really great enchant. Or, you might not get lucky and end up with something you can't use.
Some enchants that have procced:
Cogspinner Goggles of Nature Wrath
+84 Nature Damage
Cogspinner Goggles of the Bear
+59 Stamina
+39 Strength
Cogspinner Goggles of the Hierophant
+46 Stamina
+31 Spirit
+68 Healing
Power Amplification Goggles
Binds when equipped
Head Cloth
100 Armor
+46 Stamina
Durability 50 / 50
Requires Engineering (340)
Equip: Improves spell critical strike rating by 31 (1.4%).
Equip: Increases damage and healing done by magical spells and effects by up to 36.
Great goggles for casters.
Goblin Rocket Launcher
Binds when equipped
Trinket
+45 Stamina
Requires Engineering (350)
Requires Goblin Engineer
Use: Fire a powerful rocket at the enemy that does 960 to 1440 damage and stuns them for 3 sec. This thing has quite a kick though...
Cooldown: 2 min

3.5 sec cast
This baby has incredible range, and there's no mana, energy, or rage cost. You can hit someone who doesn't even know you're there. Blast flag carriers, healers, and/or ambush someone guarding the flag.
Gnomish Poultryizer
Binds when equipped
Trinket
+45 Stamina
Requires Engineering (340)
Requires Gnomish Engineer
Use: Turns the target into a chicken for 15 sec. Well, that is assuming the transmogrification polarity has not been reversed.
Cooldown: 5 min
Not only can you turn your opponent into a chicken with this trinket, but it gives you an incredible 45 stamina. The Poultryizer works on both players and mobs.
Nigh Invulnerability Belt
Binds when equipped
Waist Cloth
223 Armor
+21 Stamina
Durability 30 / 30
Requires Engineering (350)
Use: Protects you with a shield of force that stops 4000 damage for 8 sec.
"Protection not always valid. In RARE cases wearer may take additional damage."
Cooldown: 5 min
Absorbing 4000 damage in PVP can be a life saver. Using this gizmo is like having a Paladin bubble. (For Paladins, it's a second bubble!)
Like all of the quirky Engineering gadgets, strategic use of this can change the course of a battle.
Rocket Boots Xtreme
Binds when equipped
FeetLeather
196 Armor
+36 Stamina
Durability 50 / 50
Requires Engineering (330)
Equip: Increases attack power by 50.
Use: Engage the rocket boots to greatly increase your speed. You probably won't be still standing when you get there though.
Cooldown: 5 min
What the tooltip doesn't say is that these boots rocket you along at 300% movement speed for five seconds. That makes you the fastest thing in the game. You can cross from flagroom to flagroom of WSG and all anyone will see is a blur.

Furious Gizmatic Goggles
You can make eleven truly epic goggles. These headpieces are the equivalent of Tier 5 gear.
Binds when picked up
Head Plate
1296 Armor
+48 Strength
+28 Stamina
Meta Socket
Blue Socket
Socket Bonus: +4 Critical Strike Rating
Durability 100 / 100
Requires Engineering (350)
Equip: Improves hit rating by 13 (0.8%).
Equip: Improves critical strike rating by 38 (1.7%).
Equip: Allows the detection of objects that are slightly out of phase, such as the arcane vortexes of Netherstorm.
Equip: Slightly increases your stealth detection.
Use: Allows you to look far into the distance.
Let's look at some of the other epic goggles.
Justicebringer 2000 Specs
Head Plate
1296 Armor
+29 Stamina
+13 Intellect
Meta Socket
Blue Socket
Socket Bonus: +4 Spell Critical Strike Rating
Equip: Improves spell critical strike rating by 39 (1.8%).
Equip: Increases healing done by spells and effects by up to 101.
Equip: Allows the detection of objects that are slightly out of phase, such as the arcane vortexes of Netherstorm.
Equip: Slightly increases your stealth detection.
Use: Allows you to look far into the distance.
Tankatronic Goggles
Binds when picked up
Head Plate
1296 Armor
+67 Stamina
Meta Socket
Yellow Socket
Socket Bonus: +6 Stamina
Equip: Increases defense rating by +38 (16.1)
Equip: Increases your dodge rating by 22 (1.2%).
Equip: Improves hit rating by 13 (0.8%).

Equip: Allows the detection of objects that are slightly out of phase, such as the arcane vortexes of Netherstorm.
Equip: Slightly increases your stealth detection.
Use: Allows you to look far into the distance.
Destruction Holo-gogs
Binds when picked up
Head Cloth
174 Armor
+22 Stamina
+24 Intellect
Meta Socket
Blue Socket
Socket Bonus: +5 Spell Damage
Equip: Improves spell critical strike rating by 29 (1.3%).
Equip: Increases damage and healing done by magical spells and effects by up to 64.
Equip: Allows the detection of objects that are slightly out of phase, such as the arcane vortexes of Netherstorm.
Equip: Slightly increases your stealth detection.
Use: Allows you to look far into the distance.
Look up a source such as Thottbot or Wowhead for more info on these epic goggles.