Google Hangouts: Free, but need to have a gmail account.
Proficonf.com: Proficonf is a professional platform for video conferencing in real time, it works directly in the browser.
The Free plan offers up to 25 participants with no time limit for events, a file storage to 500MB, demonstration files, screen sharing.
Adobe Connect: Large scale conferencing and webinars.
GoToMeeting.com: Large scale webinar and conferencing tools.
ShowMyPC.com: Easy way to share your screen for easy over the phone tutorials.