The 9600 GT would probably be a better choice over the 8800 GS. Look for the core clock speeds when buying, the 9600 GT will have a higher core clock no matter what other than where it meets the 8800 GS at 650Mhz and they are listed at the same price, other than that the 9600 will be faster.
If you have 230$ go for a 8800 GT like Zenosincks said, it will blow those both away.
WHOOPS!!! Looks like I'm the one that messed up this time Zeno xD I've been looking at the GS rather than the GTS!
I think that the GTS is better once its core clock is 540 - 678Mhz and its memory is 512Mb or more, but your price tag goes WAY up, almost to 300$ even! You would be much better off going with a 8800 GT 512Mb.