Your best bet for the current gen of cards is the 7900GT KO from EVGA. Fairly cheap (~$300 American), extremely powerful (10% more powerful than a 7800GTX), uses little power, low heat, nice fan and heat shroud.
While ATI did serve up the most powerful cards this gen, they are large, hot, loud and ungainly. Many take up 2 slots, while the 7900GT only occupies one.
I'm in much the same situation as you. I got a X800 Vanilla this christmas, and by next Christmas or summer I'll probably upgrade to the current high end.
Don't pick up the 1st gen DX10 cards, as DX10 is a huge leap from previous DX generations and has a good margin for error (New geometry shaders, Unified shader architexture, Vista only etc).