6800 series of cards are still quite playable with a variety of games...
Personally, I don't like forking out $300-$500 for video cards or $500-$600 for cpu/mainboards all that often, and usually only do so when new games I want to play will not run at desired/acceptable resolutions with decent framerates, a strategy that has seen me progress since 1999 from a Athlon 650/GF2 MX to an XP2000+/9700Pro (2002), to my current 3500+/7800T combo (Sep 2005)...
(I suspect the debut of Conroe and Direct x 10.0/HD-DVD capable cards, mostly the former, will cause me to build yet another rig about 1.5-2 years earlier than normal!)