I like playing the first half of Tiny Wings. The soundtrack is pretty soothing, too.
iCopter is good, but the PC flash game it's based off, despite being (potentially) more than 10 years old, is infinitely better.
Draw Rider used to be fun if you can find an early (pre-November 2013) version.
Uhh, I think Radiant is cool, but they added seriously lame dialogue onto it.
I also still occasionally play Temple Run. Fun little time waster if you're waiting for somebody.