here's a comp store, its not the cheapest but they have good variet. ones you choose the card, then you can shop around to see who's got the best price.
this might be above your budget, but its good value. 6800gs $271
if you know even a little bit about overclocking, then i HIGHLY recommend you get this card, it overclocks EXTREMELY well.. most come with pipes unlocked.. its guaranteed to overclock i think. 100% success rate in overclocking, you can overclock it to x850xt pe. x800gto2 $216.60
the 6600gt you mentioned is still good value. $177
and also the x1600pro. $157.55
should give you good performance.
oh and, I JUST REALIZED THE X800GTO2 IS PCI-EXPRESS. SORRY DUDE, THAT WOULDA BEEN A GOOD CARD.