Cisco's WebEx web conferencing and desktop sharing solution is a strong and straightforward application that allows you to easily collaborate with coworkers and customers quickly and easily.
Microsoft Office Live Meeting 2007 offers web conferencing and online meeting services with a familiar Microsoft interface, and closely integrates with other Microsoft applications.
Get Started Quickly with Online Meetings and Web Conferencing
Citrix GoToMeeting is a barebones online meeting and web conferencing application that aims to get you set up and working with a minimum of overhead and training.
Adobe's Acrobat Connect Pro is a powerful collaboration and web conferencing application, with a flexible and innovative interface. However, the technology is more complex than many users will need.
SaaS Reviews 
Comprehensive Web Conferencing at a Great Price
Web Conferencing with a Microsoft Look and Feel 
Flexible and Feature-Rich Web Conferencing
Straightforward Web Conferencing and Online Meetings