Adobe Connect web meeting app - available for free for up to three participants (including host - only one who needs to sign up). Participants simply go to the host's meeting room url (which is easy to remember) and can use webcams/audio, share screen/windows, type messages and meeting notes, use the whiteboard, exchange files.
I have an account and tested it with Carl. For me - seemed to work well and could be a useful (and free) way of conducting, say, a tutorial with feedback for someone who couldn't physically be there for whatever reason. Anyone who wants to try, let me know and I'll invite you to the meeting room.
We recommended this to the folks running a Clinical Dermatology course for holding their virtual tutorials and it seemed to work pretty well. It does require quite an up to date version of the Flash player which can be a problem...i.e. anyone attempting to use a student service machine or some staff with 'managed' computers won't be able to use it. I believe Electronic Engineering have forked out for the "pro" version...or at least they have in the past. As usual with Adobe stuff,,,it looks slick!
DimDim is another web-conferencing thingy that seems to get a lot of press...haven't used it myself. Elluminate is another one that I've seen used at several meetings I've been to recently.
This is a JISC backed site covering the use of Web2.0 tools in all areas of academic practice...research, teaching and administration. It's currently looking a bit thin (July 2009) but hopefully it will get fleshed out.