Games come and go... Especially if you tear through them reasonably fast. However, a few that I am having great repeatable fun with are as follows:
Call of Duty 4: Modern Warfare
Galactic Civilizations 2: Dread Lords and Dark Avatar
Finished up World in Conflict for the PC a short while ago and I can't see myself playing it again. It was fun, but the multiplayer isn't something that I will get into. If you've played it... You'll understand that I simply can not sit through hearing the name Banon again.
Thinking about comprising a list of every game I have every played... Daunting to say the least. Perhaps I should keep it to PC only.