I work at the operations center for my university's video conferencing network. There are a lot of options out there for this, but I can't think of anything that's not expensive. Most of the good equipment I see is
Polycom. If you've got deep pockets, check them out. They have webcams as well as larger options. These aren't normal webcams, though. They do most of the video processing and compression because they're designed to operate at higher resolutions. (These look almost like you're watching TV! 8O ) To include multiple users, you'll need something to bridge the connections. There are several options. Polycom has the FX viewstations and VS4000 codecs, etc. These are pretty pricey, but think about what they're doing. Receiving and processing multiple audio and video signals, processing them, and putting them all together. Of course, if you're doing a LOT of video conferencing you might look at a Multiconferencing Unit (MCU) from Accord. These are really expensive, but they let you link up lots of endpoints in several conferences all at the same time. Sooo, there is a lot of stuff out there. The best option will obviously depend on how you plan to use it and how much you have to spend. Hope that helps.