If you want to upgrade, go for a 7800 GT or a 6800 GS. However, the 7300 GS is better than the 6600 GT you have now, so that or either of the two options I mentioned earlier would be a good choice.
"No, Mama. You can bet your sweet ass and half a titty whoever put that hit on you already got the cops in their back pocket." ~Black Dynamite