My latest gearfinder link is very simple and easy to use. I spend far too long agonising over gear and this neat tool helps me puzzle things out.
Just go to gear wishlist and enter your character name and realm. It searches wowhead, maxdps and lootrank for your class and spec and comes up with a list of items for each slot.
I'm sure it's not definitive but it will certainly help you shortlist upgrades, locate useful quest items and help decide whether an item is a true upgrade.
It uses the defaults on each of these sites and recommends that power users should go direct to them if they want to tweak the weightings to suit.