Before computers, my first love-affair with geekiness was an interest in telescopes and astronomy. For the past few years, I've slacked off considerably in my telescope making activities, but every once in a while I see something that piques my interest. Gary Honis has a fascinating webpage that details several conversions of digital SLR cameras and webcams into a form which allows them to be used for astrophotography. I found the following link to be particularly interesting for planetary photography, since the webcam is a reasonably high resolution and shoots at 30fps. For bright objects like the moon and planets, this means that you can capture moments of good seeing, and use them to generate nice pictures. Archived for future perusal:
The camera is actually very reasonably priced (only $54.03 via Amazon).