LocatePC
If you travel (or not...I had one stolen from my home!), your computer could be stolen pretty easily. LocatePC from ICONICO is free software that will send you an email message when the thief accesses the internet, giving you the information needed to track down the account used for that internet access. Given my experience, I'll probably install this one. Recommended by Kim Komando, so I trust it completely...well, as completely as I trust anything web related!