Here is a quick comparison of GoToMeeting and WebEx:

GoToMeeting
Very quick registration process
Can run meetings
Runs through firewalls
Secure Encryption
Up to 15 attendees, or up to 1000 with GoToWebinar

WebEx
Pretty much the same features
Runs over WebEx’s dedicated network

Both offer solid functionality, usability and security. Costs are simliar at around 40 bucks a month.