Ask HN: Coolest iPhone App UI/UX's? Post Your Favorite

My favorite (and their website for that matter):

http://awesome.taskrabbit.com/017e0

Twitter, Robotcat Apps (Outside Weather App), TeaApp, and despite their situation, AirBnB, all come to mind. Any others?

(email is just for new macbook air contest, you can download the app w/o it, just don't enter your email if you don't want to try to win)