It looks like Apple is working on a next generation iSight camera. The source for this (thanks MacRumors) is a QuickTime localization file which you can find here:
You can open the .strings file with either TextEdit, or a simple Quicklook, but either it its’ very clear that:
/* Next Generation USB iSight */
“iSight HD” = “iSight HD”;
Appears there plain as day. This doesn’t guarantee the release of a USB iSight HD camera, but it certainly lends a bit of validity to the idea that Apple plans to release one soon.