I often use Skype for videoconferencing. It requires a pretty powerful
computer. The video part won't work on a 6-year-old system I have, but it works
great on my AMD Phenom II X2 system.

Also, there is a commercial web site called Elluminate which is for multi-site
videoconferences. They have a free-for-personal-use version of the software
which supports up to three videoconference locations. The app is written in
Java, so it works on Linux, Windows or Mac.

I have a cheap and crummy webcam I bought in China for less than $10. It works
in Cheese, and Skype and Elluminate.