Synchronous Technology
Elluminate (www.elluminate.com) combines synchronous with asynchronous communication and allows for audio, text, and visuals simultaneously. With Elluminate, you can listen to a live presentation and view a whiteboard while communicating with the instructor and the other students.
Skype (www.skype.com) is a free program that allows audio and visual communication on the computer screen. Skype also features instant messaging, file transfer and video conferencing.
I've recently used the web conferencing software Adobe Acrobat Connect Pro at http://tryit.adobe.com/us/connectpro/webconference/?sdid=DJZHF. It seems easier to set up and easier to use than Elluminate. It has the ability to share desktops and view a whiteboard instructors can share items on their computer with their students.