ScaladoThis motion powered music player for accelerometer equipped S60 phones is probably simplest sensor based application that I have seen so far.
It provides the very basic functionality and allows you to change the music tracks with two different gestures.
Application lacks any kind of the user interface in this phase but author promised that application and interface will be improved before the official release.
This little application is created by Daniel Rocha just to show what you can do with Python for S60 and it took less than two hours to develop this minimalistic music player with sensor support.
Speaking of the functionality, shaking the phone to left advances one track in the playlist while shaking it to the right goes back one track, and putting it face down shuts down the application which is the coolest part actually ;)