There are a couple of great tools I use which may help others;

DimDim : Free, No Install, Registration required to “Host”, Voice, Video (20 people) & Desktop Sharing.

TokBox : Free, No Install, Registration required to “Host”, Voice & Video (20 people) but no Desktop Sharing.

TeamViewer : Free, Install Required, No Registration Required, Voice & Video (1-to-1).

Clearly DimDim is the winner at the moment, I’ll update if / when this changes! :-)