I'm running at 1440x900 7900GTO territory does me fine. Games like Oblivion, games running the Quake 4 engine and I'm sure Crysis/UT3 will all have options for large texture support for cards with 512MB and above.
However, people running anything over 1680 x 1050 should really go with an 8800GTX. Personally thinking of getting the standard 640MB version of this card tbh