BlinkM user, Arduino hacker, and now iPhone developer Mike Colagrosso recently got approved a really neat iPhone app called Ciao. It's a way to find and control network-connected Arduinos from an iPhone. You can even define the UI the iPhone should use in the Arduino itself. One of the examples he uses is how to control a BlinkM. Thanks Mike!
For another great use of Ciao, check out Bildr's example controlling Nixie tubes.