i recommend Logitech's QuickCam Vision Pro for Mac. its brand new and has better specs. only downside is the iSight has a better design more suited to Macs and it only use USB.
The Quick Cam Vision Pro 9000 works well with the mac despite the lack of software. I bought one new then found an iSight for $100 and picked that up. I'm selling the 9000 since I don't really need it.
The newer QuickCam Vision Pro for Mac is "Mac only" (obviously) and so it has Mac drivers. it has better Picture quality 720p than the iSight (but is more expensive) and has a light.
I was lucky enough to be able to pick up a brand new [still sealed!] iSight from eBay quite recently, the only real problem in picking 1 of these up as others have said is the cost, other than that they are quite readily available which leads me to wonder why indeed they are so expensive!