With services such as WebEx, Microsoft Live Meeting , Macromedia Breeze, and Netspoke, meeting participants are invited via E-mail to click on a prearranged link to enter the conference. The shared computer screen can be used to display a specific document or to share a Web browser to demonstrate an online application.
Robin Good mentions several cost-effective screen-sharing services that have extremely low monthly costs, offer a free trial, can be cancelled at any time, and do not generally require complex installation procedures or large software downloads.
NetOp School takes the concept of the "Virtual Office E-Meeting" to the classroom. Students located in your computer lab, across campus or anywhere in the world can log into your virtual classroom where you can broadcast your screen, multimedia files, or any of the student's screens. The entire virtual training sessions can be recorded and you can monitor students' screens as they work during a class.
InformationWeek has good list of points that you would like to answer before choosing a e-meeting solution vendor.
Q. Should I license the software or just subscribe ?
A. Depends on how often will E-meetings be held? Many services are priced by subscription rather than by individual meetings. Even if you hold meetings infrequently, it may be less costly to subscribe. For very heavy usage, licensing of software to run on your own server may be more cost-effective, but it isn't offered by every vendor. (Citrix users may want to consider their GoToMeeting product.)
Q. Will pop-up blockers stop the E-meeting software from functioning?
A. Many users have pop-up blockers installed in their browsers but don't always know how to disable them.
RealVNC is the only web based screen sharing software that is available for free. UltraVNC/TightVNC are a big improvement over regular VNC. Read this interesting SlashDot thread on choosing the right VNC Software for your job.