Buy an eVGA, you get 90 days of price protection through the step-up program. Say you buy an 8800GTS for $400US, 6 weeks later the 8900GTS comes out at $450 and the 8800GTS price drops to $300US (unlikely, but for the sake of the example), you send in your 8800GTS, eVGA credits you $400US and you pay $50US for the upgrade to the new card. Pretty sweet program. I think you might eat shipping costs.
I'm getting an 8800GTS 640MB Superclocked for this very reason, I fear that within 90 days R600 might finally come out along with the G84 refresh.