+1 to Tome of Battle, Spell Compendium, Magic Item Compendium and Expanded Psionics Handbook.
Suprised it wasn't mentioned here, but I think Rules Compendium is extremely useful. If you like campaign settings, Eberron is absolutely awesome, so you should pick it, even if you want some ideas for your own setting.
The books above I consider indispensable.
Now, for the rest, I like all environment books, the heroes books, UA (that you have already bought), MM3 (the best monsters book), and, to be honest, seems unfair with the divine / martial classes that you've bought the CArc and CMage when the classes that use it are the ones who need the least. Show some love and buy CW, CD and CAdv!