My latest obsession has been Tiny Tower. I honestly don't understand why it's so addictive. It really shouldn't be; it's not particularly fun. Then I realized it has the same build as The Sims, Farmville or Animal Crossing; some sort of weird complex that has us wanting to do virtual chores. Farmville is particularly evil when it comes to this because they charge you for it. At least Tiny Tower is free ... mostly.
Speaking of addictive games, a good friend of mine who introduced me to Tiny Tower has made an insanely fun game Mr. Runner 2. Check it out! He also just started working at Zynga, so you can thank him for all that evil Farmville nonsense.