Lap timer
Bought this lap timer app yesterday and trailed it today at Sydney Motorsport park. Now, I'm no techie expert, in fact, I'm an absolute technomoron, but this app worked faultlessly from the moment the flag drop. So easy. Just set the circuit you are at, and press the "go" button, and leave your iPhone somewhere secure in the car and voila, every lap time recorded. I can strongly recommend this app for those that don't want to spend several hundred $$ on a standalone unit.