I recently re-downloaded an indie game called Oasis and have been playing it during my commute. It is a casual game, but it has all the elements of a really solid gaming experience. I recommend trying the demo, at $6.99 it's a little expensive for what it is (and most places try to charge $20 for it! so if you try the demo and like it, find a place where it is only $6.99) but if you have some disposable income its worth the price.
It's an exploration/strategy game..I think it was best described as "civilization meets minesweeper" in 5 - 10 minute rounds.
I also can never recommend Toribash enough, its a really really technical turn-based fighting game where you make up your own moves based on specific muscle area tweaking...hard to describe, but its free! Try it out, get frustrated, go online and watch how good people are, get inspired, play it way too much, tooooribaaash!
Oasis:
OASIS | Mind Control Software
Toribash:
Toribash - Violence Perfected - A physics based fighting game.
If anyone tries these, even if you hate them, I'd love to hear your feedback.