I would highly suggest Magic TG: Duels of the Planeswalkers 2012. Its not a really hardcore game, its turn-based, and it doesn't require a long time commitment. Even if you've never played Magic before (or are horrible at it, like me) its still a fun game to play when you have a half hour here or there.

I recently bought Europa Universalis 3: Chronicles and I think (for me personally anyway) that its very relaxing. The initial learning curve may be a little steep (not as bad as the screenshots make it look), but its definately a "take your time and do things at your own pace" kind of game. The game is designed incredibly well, and the AI is also very intelligent (much much better than Total War games) Plus, its on sale now on steam for $7.50!