I have a Sony TRV-250, it is a Digital Camcorder that has Video out, USB out, and FireWire out/in. The USB function is listed primarily for doing what you want to do, a high quality USB webcam, where as the FireWire is for transferring raw video data from tapes to your harddrive. I'm not sure about streaming via FireWire, but as I said, the USB function is for doing just what you are saying here, and it is quite high quality.

I'm not sure how much you're looking to spend but this is the lowest level camera in the series and it's a $400 camcorder, so, thats a price point for you. I do more digital video type stuff rather than need it for a webcam so I'm probably upgrading to one of the new series Sony MiniDV cameras because they have slightly better resolution, but mostly because I need external audio (the TRV-250 only alllows for using the onboard stereo mic )

if you have anymore questions, i'm happy to answer them to the best of my knowledge, I love DV stuff!