Black Ops is definitely high on the list. I also really like Dead Space 1 and 2. Fallout 3 is another great one. I want to add Soul Caliber 4 and Marvel vs Capcom series too
What's so great about those games is that you can play them for hours on end. It depends what genre you like.
If you're paying $60 for a game then you want to be able to play it for a while