A quick re-test of this bargain 720p HD webcam from RocketFish led me to come up with it the best Apple compatible CHEAP webcam choice. It has a surprisingly clear and sharp image, good color balance, and a smooth auto-focus that isn't slow to respond like other cheapo AF cams I've tested. Decent-sounding microphone too. Quite a deal for around twenty bucks.
For about five dollars more, the Mac compatible Logitech C310 is superior to the cameras in it's C1XX and C2XX series range. Most notably it has a higher resolution sensor and supports RightLight2(tm) which adapts to low-light situations better than cheaper Logitech cameras without it. It's a Fixed-Focus camera with noise-canceling microphone. It's image is as good as or better than most built-in Apple iSight cameras with far greater flexibility in camera placement, angles and positioning.
When you go beyond 720p into 1080p HD mode you need A LOT of CPU horsepower AND internet bandwidth to handle a staggering amount of image data. So these 720p HD cameras have good frame-rates in every Mac video capture and conferencing app I tried. They also have a built-in microphone that sounds fairly decent - and as such are all good choices for a cheap Mac webcam with microphone solution for desktop Macs which don't come with any microphone at all, like the Mac mini and Macintosh Pro tower.