I mounted my old Canon S30 camera on the windshield to automatically take photographs of anything interesting that might happen on the road. The camera is USB-controlled by my notebook computer, and set up to take a photo once every 10 seconds.
The software I use to control the camera is G2Remote, an older program that still works pretty well. You plug in a USB cable, and the software takes photos every few seconds. They can be downloaded to your computer rather than stored on your camera memory card.
It's fun to get photos of places where I would normally feel awkward pulling out a camera, like military inspection stops and border crossings. Someday I'd love to have 4 cameras, pointing in all directions!
I can later put all these photographs together into a time-lapse movie using Apple's QuickTime Pro.