This question shows how to compare items in the auction house with what you are wearing, but for me that's not always enough.
When I'm comparing a +damage ring with a +attack speed ring with a +stat ring, I have no idea how it will affect my overall DPS. The tooltips in the auction house don't show the stat differential like items do in-game.
Is there a way to see the change in Life, Damage and Protection on an item in the auction house before you buy it?