Tinychat is a powerful service that offers a lot of web meet-up power from one link you share with participants. Once they arrive, participants can stream webcam video and audio, display desktop portions, share files and talk in plain old text.
It's an impressive amount of multimedia for the free portion of a web service, and, in two tests, most of it actually worked. Lifehacker editors could hear audio from each others' microphones, video streaming worked when it was available, and desktop sharing worked, at least for those with Java plug-ins installed. Web site owners can also embed an ongoing Tinychat room into their blogs or sites, with most of the same features.
There's no way to password-protect the rooms without a paid ($9.95/month) Pro account, and it should be made more apparent that "signing in" with your Twitter username actually broadcasts your chat room location on your Twitter feed. But given the hop-in, hop-out nature of a Tinychat room, it's relatively safe to hand out a URL to just those folks you want chatting and use the room for what you need. A Pro account also allows for the naming and preserving of five rooms, saving of chat transcripts and streams, and HD-quality video.
Tinychat is a free service, no sign-up required to use it. Looking for a more controlled, perhaps business-like environment to talk on the web? Try the recently featured drop.io variant presentation.io.