I've used a tool called BigBlueButton, which is a free (and open-source) conferencing tool. It's still under development, but I'm in the process of integrating it into my office's extranet as a replacement for GoToMeeting.
It can act as a stand-alone tool (i.e., you download the VM and run the conferencing tool on your desktop or server for privacy), or you may be able to jump onto their "demo" site, and create yourself a private meeting for a short time.
BigBlueButton contains a combination of Asterisk, Red5, and may other tools, and is aimed at the educational market - it allows for uploading presentations, a whiteboard, and all participants can have a webcam active.
You can see the main website for it at: http://bigbluebutton.org/
And the Google Code repository at: http://code.google.com/p/bigbluebutton/