Measure everything that vibrates, shakes or moves. Or why not an actual earthquake?
Seismometer uses your iPhone's built in accelerometer to measure movements in two axes, calculate the resulting energy and draw the results on a rolling logarithmic scale.
* Different signal filters
* Highly configurable
* CSV exporting of recordings
* UDP Streaming
http://yellowagents.com/seismometer/ for more info and examples of how to use the streaming protocol.