As an engineer, there are many addons you can use to make crafting easier. However, the sheer amount of addons is overwhelming and not all of them play nice with eachother. For this reason I'm going to list several nifty addons that do work nicely and make your life as an engineer a little easier.
Before I do that, let me share a few safety related info chunks:
●When you download a file from a site, even one you trust, make sure to scan it. Even large, well known addon sites get infected with trojans occassionaly.
●Legitimate WoW addons do not use .exe files. Stay away from these, they are risky business.
Skillet
This addon changes your profession window to be larger and more user friendly. When you select a schematic in the list, the materials will show up on the right. You can click components to see what you need to make them. You can queue a schematic and see a shopping list of all the materials you'll need to craft that item.
You can even set the addon to automatically purchase vendor-bought items on your list when speaking to a vendor that sells them.
Download it here (wowinterface)
Tradejunkie
Tradejunkie provides information on where to get schematics. At the time of this writing, the addon contains several flaws. Some schematics that are not obtainable in game are listed. Gnomish and Goblin schematics aren't listed either; A small issue as those all come from the same trainers.
The addon is handy enough to make up for its shortcomings. And hopefully those flaws will be ironed out soon.
Download it here (wowinterface)
mirror (worldofwar.net)
Gatherer

Gatherer has been around for a long time and remains an extremely useful mining addon. It shows possible ore and/or herb locations on the worldmap and minimap. Its seen large improvements from its first

incarnation. In addition to ore and herbs it can show various quest item spawns and treasure chests spawns. If you just want ore, you can disable the rest.
I recommend you install both Gatherer and the wowhead database addon. When you import the wowhead data you will find all the nodes right there on the map.
Download both Gatherer and GathererDB here.
These are a few of many useful addons out there. Keep in mind that having your entire interface fall to pieces when a patch comes out is not a very pleasant surprise. I suggest to always try and keep the amount of addons you install to a minimum.