I got a cheap webcam off eBay:
The camera works fine. IR range is only about 6", so "night vision" is really only a dream (those LEDs are IR LEDs). Viewing angle is limited. Eh, it was $0.99, plus $10 shipping.
The Dorgem software however, is not friendly, and I'm not convinced that the "motion detection" feature is working quite correctly. The camera is curently sitting right under my monitor, so may be picking up some intereference there; I'll re-locate and report results.
Otherwise SourceForge has plenty of other choices for the same task.