If you're fortunate enough to have a built-in iSight camera in your Mac, this won't be of use to you. However, if you have a standalone iSight perhaps you'll find this interesting.
I recently purchased Kaidan's iSight Accessory Kit. I decided to do this because I wanted more flexibility in positioning the camera, which has a fairly narrow field of view, and I already had a wideangle lens that I use for my panoramic VR projects so this kit allowed me to get more use out of the lens. (How's that for a textbook case of cost rationalization?)
You can buy each item in the kit individually. Here's my quick review of each piece.
These two snapshots, taken from exactly the same camera position, show the difference between a standard iSight and what I get when using my lens. It's working well for me, and I've found that I don't really noticed the corner vignetting. The wider view definitely makes video conferencing more comfortable because I spend less time making sure I'm in-frame.