Wait for the next card release, then the older ones will be cheaper.
No point in buying just yet. There are some bargains to be had, like the 6800GS, especially if you buy two in SLI (assuming you don't have an AGP motherboard, which IIRC you do).
the newer cards will have more unified shading units, which should suit later games (like F.E.A.R. and games yet to be released), so buying a current card will just be a stop-gap ... after all the 6800 has been out for yonks.