Your system will be able to run any game on the market with graphics turned all the way up due to the resolution you'll be playing at.
Call of Duty: Modern Warfare 2 is very easy to recommend if you like multiplayer FPS games. It looks very good with the graphics maxed out.
Dragon Age: Origins is a traditional RPG where you control a group of characters as they fight through various dungeons. It's very, very good and you'll like it if you liked any other games in the genre (D&D, Baldur's Gate, Final Fantasy). The graphics are aimed at realism and aren't very stylish as a result, but the story is why this game excels.
Borderlands (RPG/FPS) is a great hybrid if you have a friend to play it with. It's alright solo, but the cooperative gameplay is what turns it into an excellent game. The graphics are much more stylish but you may want to check out a preview first because some people love them and some people hate them.
Torchlight is a cheap little Diablo clone that manages to be great by removing a lot of the tedium and really giving you the feeling of being powerful by killing 20 enemies in a couple of seconds. Graphics are decent but not great.
Dawn of Discovery (Anno 1404) is a slow paced city builder like SimCity where you establish a colony in the Orient in 1404 and try to build it up to a large city. I've always liked the genre but the Anno series in particular is really good with the emphasis on trade routes.
Fallout 3 is a really great RPG/FPS with a poorly written main plot arc and perhaps my least favorite ending of any game. It's worth playing but I wouldn't prioritize it.