Heya,
The now 3 year old 8800GT (or 9800GT, same card) will do that resolution, with AA enabled, perfectly fine in nearly all games you play (the exceptionally piss poor coded Crysis being the kind of game it won't do that with AA enabled, but you can play it perfectly find at med/high details at that resolution in Crysis with no AA just fine!).
The HD4850 will certainly do the job.
Higher memory cards (1gig for example) and faster cards will be more appropriate if you want to turn on advanced things like AA and AF and higher quality textures (if available in the game).
But at that resolution, nearly any modern card will do it perfectly well.
$100 for a 9800GT
$130 for an HD4850
If you spend more than that, you might as well look at the GTX260 and HD4870 as they're both in the $200 range now.
Cheers,