If you have an 8500GT you should probably upgrade... consider those:
8800GT with custom fan (needed) and 512MB by ASUS (decent company): 120$ -20$ MIR +0 shipping.
http://www.newegg.com/Product/...x?Item=N82E16814121263
4850 with custom fan (needed) and 512MB by MSI (decent company): 195$- 30$ MIR + 9$ shipping.
http://www.newegg.com/Product/...x?Item=N82E16814127370
Or you can get a GTX260, a 4870 etc with the default fan, from anyone... either of them for 230$ or so is a good buy. but from what I see they are about 250$ at the moment.
The GTX280 is still too expensive IMAO. And doesn't really give all that much.
The 4870x2 is too expensive, but does give a significan't boost. But I wouldn't get it unless you are using an LCD which is 27 inches in size or above.
check out this chart to see about how powerful your GPU is:
http://www.tomshardware.com/ch...4%2C1605%2C1617%2C1563
Make sure to look out for OC (overclocked) SLI (two cards of same type working together from nvidia) or CF (two cards of same type working together from AMD). Those can throw you off, don't just look at the name. Also pay attention to how much ram the video card in question has.
the 8500GT gets a compounded total FPS in all tests of 500, the 8800GT OC is 2150 and the 8800GTS 320 is 2000, the 8800GT I suggested is between those two cards.
So the 8800GT is slightly over 4 times faster then your current video card.
the 4850 is about 20% faster then the 8800GT, the 4870 and the GTX260 are about 20% faster then the 4850.
PS.
Both the 8800GT and the 4850 need a custom fan or they will be very loud and run too hot, which is detrimental if you want trouble free operation. So be careful about which model you buy. The ones I linked have such a custom fan, and are from reputable companies