Dead Space is indeed Jaw dropping, and looks better on a monitor I think basically because you sit closer. I played in in XP and it looks great, but, unfortunately, it has some minor problems with VSync, causing the mouse to go crazy on a lot of PC's. Fallout 3 is nice, if you like browns and greys. It's basically Oblivion with Guns, really. :-) Mass Effect will tax your system a lot, and will look good doing it. Either of the Crysis games will attempt to bring your computer to tears and beat it with it's own keboard cord. From what I understand, they aren't coded the best. I've only played warhead in Vista, and it ran kinda like a pig. However, I don't have the greatest system known to man. My Vista score is only a 5.6. Basically any of the newest games that are out that strike your fancy, check a review to make sure you don't get something you will hate, pick up a copy and play to your hearts content.
Nathan