This DIY project takes an old webcam and converts it into a motion sensitive CCTV camera, complete with email and Growl/Prowl push notifications.
Though it might sound complicated to create your own motion-sensing surveillance camera, UK hacker Sean's directions show it's a pretty straightforward project that really only requires the webcam (you probably have an old one lying around somewhere), an always-on PC, and free software. (If you want Growl/Prowl push notifications to your iOS device you'll also need that software.)
Sean mounted his old webcam using right angle brackets, then routed the USB cable to his server. The Yawcam free software provided a camera feed over his local network, as well as an external output so he could view the feed from anywhere else with a web browser.
Email notification, with still captures, is enabled from the motion detection configuration settings of the software, and you can set up Growl notifications as well.
All in all, seems like a fun geeky project to do that could also be very useful. See the blog post below for the full instructions.