Just a note that in December 2006, I installed and evaluated the latest versions of Skype for Mac and PC. I tested interoperability between Mac and PC, and video conferencing. I recommend Skype because of interoperability and the large international user base.
I also looked at web cameras. There are a lot of them. I studied specifications and reviews of Microsoft and Logitech products. The pricier models appear better. However, while bulkier, inexpensive digital camcorders provide the best quality and feature set. As far as web cameras per se, Apple’s iSight provides the best quality and feature set on the Mac.