My newest and coolest (imo) iPhone app is called Dynolicious. They market it as a dyno in your pocket and so far its been pretty damn solid. It uses the weight of your car along with the iPhones built in accelerometer to give you 0-60, 0-100, 1/4 miles run times, braking times and distances, how many G's your pulling while accelerating, braking and cornering, and even how much horsepower your putting out at the engine and at the wheels. It's off by a +/-0.08 which is outstanding for a lil $12 dyno in your pocket
I think its a very cool way to tap into the potential of an iPhone.
http://dynolicious.com/
Pandora fuckin rocks, too!