Telekinesis is an early version of a Mac OS X application that allows you to interact with your Mac from your iPhone:
Stream music and videos from your computer (0.9.8)
Screen capture with mouse click and basic typing support
Simple iTunes Remote control
Browse your files
Run applescript remotely
iSight image capture
The software is still in a very early version (alpha) and there are security implications in opening up your Mac in this manner, but is a proof of concept that should open up future development down the line.