"YouTube for Schools brings the power of video to your classrooms for free. Access thousands of free high quality educational videos on YouTube in a controlled environment"
Yugma provides desktop sharing, chat and white-boarding. It also supports VOIP conferencing, including a feature that integrates seminars with Skype calls. Presenters can use PC, Macs or Linux. Participants can use almost any system or browser by downloading a Java applet. A free, limited-functionality version allows up to 10 people to participate; more feature-rich versions start at about $200 per year for up to 20 people
While focused more on desktop support situations, TeamViewer allows presenters to share PC or Mac desktops with participants on PCs or Macs. Both presenters and viewers must download and install an application-making it more appropriate for internal teams than more public situations. A free version of the tool is available for private use; otherwise it starts at about $250 for six months.