Or, at least like to still play on and off, this doesn't (have to) mean a game where you play every week, or every month, but it has to be a game that you like to play every year. I have quite a few, but I'd like to know what yours are. This is from 2005 to now (PC or this gen consoles), but I'd prefer if it weren't from last year. It can be, but I prefer it weren't.
Original Crackdown, go back every once and a while to throw cars into water, driver my car under other cars to launch them into the sky, and just general dicking around.
Whatever the latest major Pokemon game is (Pearl until Platinum, then Black replaced Platinum).
Final Fantasy 12 (since it technically came out this gen), limitless ways to experiment with the combat makes every play through a different experience for me.
Gears of War 2 as well, but, since I only have a couple of achievements left in it I haven't really touched it in a while.
Too many for me to list really, but here are some I most often come back to and spend a ton of time in.
Deep Fighter PC (Still haven't beaten this, Damn it's hard)
Homeworld 2 and it's various mods