As far as I know, Logitech only has two compatible webcams for Mac OS X and they're the older version of the Notebook webcam and the QuickCam Pro 4000. They're rather expensive, especially considering the quality.
Once getting a USB-connected webcam, you still need to buy an iChat plug-in, ichatusb, I believe, to make the webcam work with iChat. Yahoo! Messenger 2.3.8 will probably recognise them, though.