I use my miniDV camcorder as my FireWire webcam - it works brilliantly. If you don't want the inconvenient power-off after 5 minutes, then take the tape out of the camera. It'll stay on then.
Otherwise, you could go for one of those "FireBot" web cameras, or the FireWire version of the iRez Kritter. They're all pretty much the same - the price should be fairly similar, too.