So lately I've been looking for games to play when I'm extremely tired or half focused. I've wanted to have several games to play while listening to podcasts or when I'm unwilling to exert any mental effort. The main selling point is that it has to be easy to pick up gameplay, with little emphasis on story or atmosphere. I started Borderlands with the intention of doing this, but I could never bring myself to actually enjoy it. So I have come to the Giant Bomb forums, asking those with much more experience than me for suggestions.
Trials Evolution seems this way. I've only played the demo, though.
Not these games. Not to me anyway. They are far to hectic to be mindless.
I would say Journey, Flower, Beyond Good and Evil, Enslaved, the two DeBlob games, and Kameo come to mind.
@Willin: Just Cause 2 really is the poster-child of "mindless fun" games. I came into this thread expecting people would have recommended it right off the bat, and was shocked to see it absent from the first page. The fact it's also dirt cheap at this point makes it a perfect title to pick up and enjoy without having to feel any commitment to it.