Item Information

Lootzor allows you to search for items according to your most preferred statistics. You can restrict the items to only those that drop from instances that are accessible to you. It claims to search for gems as well but I have not had that work yet.

WoW Gem allows you to search for gems according to the stats they give, the rarity, and bopness. The searching is not as good as lootzor but it is quicker.

Be Imba assesses your character and provides hints for improvement. It is very rarely completely satisfied. Also, the parry cap is considered to be 6.5% not 5.5% so adjust accordingly. Most useful thing is the assessment of the instances you can handle. I cannot guarantee the accuracy of that

Warcrafter Sandbox allows you to configure a toon with specific equipment and assess the result. Not as good as it sounds, but still good.

Berg's Tank Gear Ratings. Only for warrior tanks. Assesses gear according to effective health and includes avoidance. Also assesses gems and enchants, and provides notable critiques. Tank gear ratings are always hotly contested so don't consider this definitive.

Petopia. Only for Hunters. Pet information of all kinds. I guess a pet is an item for a Hunter

Shadow Panther. Only for Rogues. Ranks gear for PVE and PVP. This is a good starting point but remember that the fixed MAEP formula is only an estimate (see this thread for more information).