Mmm first thing that came to mind was FEAR. I would recommend ignoring graphics specifications when you buy your games. Your comp obviously wont be able to handle the highest settings on newer games, but I have no doubt that you will be able to play any game out there.
Just grab some games that you have heard have great gameplay...and don't forget to get a copy of Crysis...even though the release date has seemed to suspiciously move back a couple more months.
I would also recommend using XP for your games. I don't know if you already have it or dual boot or something, but if your wanting to get the most out of your system (and aren't shooting for DX10) then a memory-efficient OS would be the way to go.
Happy hunting; sorry that I can't name specific games, but for that I would just look on a gaming web site and see what's popular.