I'd go with a 8800gt, when it comes out. It's looking like it'll beat an 8800gts, from a few posts today. Not sure how acturate that these posts are, so I'm not ready to pull the trigger on the idea, but nVdia has had a year to make something better.
Looking at the tread name i thought you were talking GTS versus 2 SLI 8800GT which i was going to say the SLIed option but the GTS will easily defeat SLI 8600 cards.
To note: The GTS 320MB are rumoured to be discontinued once the 8800GT comes out as well as the 640MB version getting some more shaders (rumoured). It might be worth while holding out too see what happens its only a few weeks out of the release and an 8800GT or the revised 8800GTS 640MB will be better options.
what??? Never heard that before!! I know you can have 2 dif cards for running different monitors and apps etc, but in crossfire?? You meen, the 2600 would accelerate the performance of the 2900?? That doesn't sound possible.