I came across a new free site which provides basic screen sharing. It’s much cheaper and easier to use than WebEx, although it is a fairly basic tool at the moment. However, if you want to present or demonstrate remotely it seems to be up to the job. Check it out at http://www.screenleap.com/.
The one caveat I should state is that it’s not completely secure (as in principle someone could “guess” a meeting number) but I don’t think it’s any worse than WebEx in that respect, and it’s a lot simpler to use.