I had a logitech one that was mac-compatibale I'm pretty sure is was the Pro 4000 model, I'd have to check on that though. I used it with an imac and never had any problems.
This could be useful. I used this plugin with old QuickCam Express, worked for Skype, poorly for Delicious Library, but it doesn't work with iChat or iMovie.
I for one, am looking forward to Apple relaunching a revised external iSight.