Yugma and WebHuddle, two offerings I've tried in the recent past is just the right ones for you.
Yugma has to offer the following cool features...
- Instant real-time desktop sharing
- Virtual meetings and web conferencing
- Whiteboard, annotate and share files
- Windows, Mac and Linux compatible
- Invite up to 10 people for free
- Free teleconferencing
WebHuddle, on the other side is something similar to Yugma, and offers its own set of value-addons. You may want to check out the WebHuddle demo site here.