Need a little extra motivation to help you tackle your to-do list? Carrot ($1) should do nicely. Touted as a to-do list "with a personality", this moody little app will reward you when you're being productive, while greeting you with a clean, white/black/blue interface. Start slacking, however, and you'll be greeted by an angry app, complete with a black/white/red interface and not-so-subtle hints that you need to stop being so lazy. With over 300 rewards and two full "chapters" to unlock, it's like a game inside a productivity app.