Probably a collaboration of all the NHL games since 1994 - I've never missed one. I also had played all the Pokemon games until this most recent batch, that's a time sink too.
Most recently (last few years) probably WoW. I played that just about every day for the past couple of years until I quit a month or two ago. No more guild, no more raiding, nothing left to really do, neh? Dragon Age: Origins is my current fix and DA2 is out in March, I believe. I enjoy it.