1) Soul Calibur. Probably the definition of a Comfort Game, but it was extremely fun. I never really played multiplayer, but the single player mode was enough for a ridiculous amount of fun
2) Sonic Adventure. A somewhat odd choice, but to this very day, I will pop the disc in and run through a few levels and bosses. Playing the Lost Highway stage will make any day much better.
3)Rome: Total War. Another odd choice, considering the depth of this game, but I honestly will still go and play the campaign mode when I get home and just veg out in front of it.
4)Homeworld 2. Now, I haven't played this in a while, but since it came out to whenever I stopped, I would go through the custom battle mode constantly. It had a somewhat throw away story at times, but the use of the third dimension for RTS maneuvring was very fun.
5) Advance Wars. Yes, a third strategy game. It's not so much that I love strategy games, as they're a big part of my quick play template. I love to go in and play a level of this amazingly fun and stylish game just a bit every now and again.