Here is all the hard information and what it means to shamans. This is from their point of view, and how it applies to them at level 70. Some of the numbers are less or more depending on your level. All numbers are accurate at the time of the writing of this guide, but Blizzard can change these at any time.
Strength
Strength gives you two melee attack power per point of strength. Strength also increases how much damage you block with a shield.
Strength is an ability that shamans who are going with an enhancement specialization might want to get, due to it helping with damage and chance to hit. Elemental and Restoration shamans can use strength to increase their damage blocked with a shield, but you should never sacrifice intellect, stamina, or spirit for strength.
Agility
Agility gives you two points of armor for every one point of agility. Agility increases your chance to critical hit with melee weapons, your chance to dodge attacks, and your chance to parry attacks, if you have the ability. Agility is an important base stat for enhancement shamans. Increasing your change to get a critical hit means the enhancement abilities like Shamanistic Focus, Flurry, and Unleashed Rage will go off.
Stamina
Stamina gives you 10 Hit points per point of stamina. Taurens receive 10.5 hp per point of stamina.
Stamina is one of the most important base stats. All three classifications of shamans can use more hit points. There are times when a healer, or DPS, might pull too much threat and end up getting hit a few times. You need to be able to survive these few hits until the tank can get back on the top of the threat list. If you are off-tanking, or trying to be the main tank, it is obvious why you need the added hit points.
Intellect
Intellect gives 15 mana per point of intellect. Intellect also gives you a 1% chance to critically hit with a spell for every 80 points of intellect. It also increases the rate that you learn new weapons skills.
Shamans should count this as their other base stat to get up high. The increase in mana pool, the increased chance to critically hit with both offensive and healing spells is beneficial to all shaman builds.
Spirit
Spirit increases the regeneration of both mana and hit points.
Mana is regenerated at a rate of Spirit/5+15 per tick (2 seconds). There is something known as the five second rule with mana regeneration. Mana from spirit is not regenerated while casting a spell and for five seconds after the spell is complete.
Hit points are regenerated at a rate of Spirit*0.11+11 per tick. Trolls regenerate at 110% of this. Hit points are not regenerated during combat.
Spirit is more important than strength for elemental and restoration shamans. For enhancement shamans Spirit is the least useful base stat. The inability to regenerate mana for five seconds after casting makes it useless regeneration if you are chain casting spells. The hit point regeneration is not effective while fighting. Spirit helps a lot with down time while leveling. Once you are not doing a lot of solo leveling, spirit goes to the back burner for importance.
Armor
Armor reduces the damage you take when hit with a physical attack. Armor has diminished returns on the amount you wear and by what percent the damage you receive is reduced. I recommend looking at the following chart:
(http://www.wowwiki.com/Image:Armor.JPG
Armor is important to shamans. At level 40, shamans are able to wear the second highest type of armor, mail armor. Before then you are only able to wear cloth and leather. Enhancement shamans need as much armor as they can get, due to the fact that you are going to be getting hit a lot while playing. DPS shamans and Healing shamans need the armor if they pull too much threat from the mob. Shields are commonly overlooked when you consider armor. Some shields can nearly double your armor total. Also, armor is important but don't go adding an armor enchantment when you have the option of intellect or stamina.
+ To Spell Damage/ Healing
Equipment that gives + to spell damage and healing has the clause “up to” in it. That means that the baseline that a spell will receive is said number. Spells with a fast cast time will get less than the amount, while spells with a very long cast time get a higher amount than the bonus number.
This type of gear is very important to both elemental and restoration shamans. This is a stat that you can never get enough of. Enhancement shamans gain from having this type of equipment, but casting is secondary to their melee power.
Attack Power (AP)
Attack power increases your melee DPS (Damage per second) at a rate of 14 AP = +1 to DPS.
Enhancement shamans will find this to be a very important stat to increase due to the fact that this directly increases your damage output. It is not nearly as important for restoration and elemental shamans.
Critical Strike Rating
Your chance to critically hit with a melee weapon is based on your agility. Critical strike rating increases your chance to get a critical strike by one percent per 22.1 critical strike rating points. Critical strikes are figured at level 70 and versus a level 70 mob.
Like attack power, critical strike is important for Enhancement shamans. It will increase their total DPS over time on a mob
Spell Critical Strike Rating
Your chance to critically hit with a spell is based on your intelligence. Spell critical strike rating increases your chance to get a critical strike with a spell by one percent per 22.1 spell critical strike rating.
This ability is important to both enhancement and restoration shamans. Elemental shamans get an ability called Elemental focus, which makes it so that the next spell after a critical spell strike is at 60% of the mana cost. This makes Critical strike rating important for saving mana. Restoration shamans get an ability called Ancestral healing, which makes it so that the target of a critical heal gains between 8%-25% of an armor increase, depending on how many talent points you put in to Ancestral healing.
Defense
Defense rating items increases your chance to be missed, block, dodge, and parry an attack. The improvement is one percent increase per 25 points over the mob's base attack skill.
This is an important skill for enhancement shamans. This will help further mitigate damage.
Resilience
No characters have any level of resilience by default. Resilience is gained through items, enchantments and elixirs. One point of Resilience gives you -0.025% chance to be critically hit, and it gives a -0.05% damage reduction to critical hit damage, and damage over time spells.
Resilience is a very important PvP statistic. A lot of damage in PvP fights will come from critical hits. The ability to mitigate this damage greatly improves survivability.
Spell Resistance
There are five types of magic resistance: Arcane, Fire, Nature, Frost, and Shadow. When an offensive spell hits you, a roll in the background is done based on your resistance to the type of spell that hit you. The roll determines if it is 100% resisted, 75%, 50%, 25%, or none. The cap for resistance is 75% average of the damage mitigated. The cap is five*level of mob. For a level 70 mob it would be 350 resistance.
Mana Regeneration
Some items have mana regeneration on them. This is called MP5 regeneration. The best part about MP5 equipment is that it continues to work during the five second rule.
This is an important ability to have on equipment for elemental and restoration shamans, the main reason being that all the regeneration happens even while chain casting spells.