Hi-
With Leopard, you can run most any USB webcam, without additional drivers, whether the camera is "Mac" compatible, or not. My Logitech Quickcam Ultra works great in Leopard!
To work with iChat, in Tiger, the ichatUSBcam driver helped out (Skype didn't need drivers):
http://www.ecamm.com/mac/ichatusbcam/
Check out the QuickCam line from Logitech. They have some very reasonably priced, good performing products.
MacAlly also makes a Mac compatible webcam.
The following is a list of cameras that are usable on a Mac, and compatible with Skype. note, that this list is pre-leopard:
http://forum.skype.com/index.php?showtopic=69289