I am also thinking og moving up from my EVGA 8800 GTS 512 mb. Seems when I push my e8400 to 4 GHz (8 X 500 fsb) my old 8800 GTS starts to bottleneck.
I would wait at least 2 weeks to see if prices come down on the GTX 260 - 216 core models. It's a waste to upgrade to the 9800 GTX+ because you'd be spending $150 for at most a 5% performance gain. I wouldn't buy the 4870 either (bad drivers, heat issues, rendering issues - leaving out textures) http://www.madshrimps.be/vbulletin/f22/why-my-camo-cover-missing-ati-hd4000-rendering-issues-dx9-62720/
For $178.99 w/free shipping get a brand new GTX 260 (216 cores) from Newegg. http://www.newegg.com/Product/Product.aspx?Item=N82E16814143155
I'm betting that the GTX 275s will be under $200 in 3 months or less and that's what I'll be upgrading to.
Watch out and don't by the old EVGA GTX 260s with only 192 cores!