xune
iPF Noob
Recover a stolen Mac with free tracking software
More info > Hidden - The most advanced theft tracking software for your Mac.
Note: Their website recommends a firmware password to prevent a clean reinstall, incase a thief attempts to remove the tracking software. Apple's support site explains how to do that. Setting up firmware password protection in Mac OS X

cnet said:Today's deal won't sell out (though it will end in a couple weeks). It's called Hidden, and it's a tracking utility and service for Mac systems.
Normally it costs $20, but you can get a Hidden license free until Jan. 1, 2011.
Just to clarify, the license doesn't expire on Jan. 1--the offer does. Once you've installed and registered the software, it's yours to keep for life. No subscriptions, no renewals, no Hidden (pun intended) charges.
When you activate tracking, Hidden will locate your stolen computer anywhere on the planet, collect photos of the thief and screen shots of the computer in use. (We also collect lots of nerdy network information, but we won?t bore you with the details!)
The Hidden team will also help you work with the police when recovering your stolen computer.
More info > Hidden - The most advanced theft tracking software for your Mac.
Note: Their website recommends a firmware password to prevent a clean reinstall, incase a thief attempts to remove the tracking software. Apple's support site explains how to do that. Setting up firmware password protection in Mac OS X