There are many reasons why you should use Chatrandom.
Some of the more expensive models do fancy things, like tracking (the camera follows you around the room) and have nice zooms, which may be useful, depending on your intended use.
I've included a photo of the Creative Web Cam Vista Plus, which is a really cheap, very basic webcam, which is Mac and PC compatible.
(It's hard to find a webcam without a microphone, actually, but if you're buying a really cheap one, do check!
) It's worthwhile going to a large computer store (Comp USA, Compusmart, Future Shop, Best Buy, or whatever's large and near you) to have a look, as they tend to have one of each webcam set up and connected to a computer, so you can compare image quality.
They have also become a source of security and privacy issues, as some built-in webcams can be remotely activated by spyware.