EquipCompare
http://www.curse-gaming.com/en/wow/addons-308-1-equipcompare.html
Forget hemming and hawing over whether or not that two-handed axe is better than the two-handed sword you're currently toting - EquipCompare will help you decide. Whenever you mouse-over an item, EquipCompare will pop up windows showing already-equipped items that occupy the same equipment slot. Don't hassle with opening up your character window and painstakingly pouring over your item slots in order to figure out whether or not you want to buy something from the Auction House. Groups hate it when you lag over a roll while deciding whether to "need" or "greed" some fancy new piece of armor. Now, you'll know almost immediately.
