PDAnet - tether to your laptop/pc to use your phone as a modem if you're on the road
SlideIT - works just like swype, the text input program that set the world record in the commercial. It's free and it's available, unlike swype
ConvertPad - converts a ton of stuff such as volume, temperature, distance, etc
LED Light - uses the camera LED's as a flashlight, pretty nifty to have
Compass - heading, longitude/latitude, altitude, pitch, roll
GPS speedo - if your cars speedo craps out I suppose. It was spot on with my trucks speedo
Shooter - ballistics calculator if you do any long range shooting