Some recent goodies from the app store:

Dual level (a 2-axis spirit level)
Airsharing (Killer app for copying files between iphone and PC over wifi)
Flight Tracker (brilliant flight checker which tells you dept/arr times, gate and even if the baggage is in the hall)
CityGuide (A worldwide city guide - right now it only covers CH which suits me fine )
Trailguru (Register for an account and then have all your GPS data synced with their server and over-displayed on a googlemap)