Quick Screen Share

QuickScreenShare.com is the simplest way to share screens with anybody:

No registration required and completely free. Nothing to install for sharer or sharee (assuming you have Java). Works on Windows, Mac, and Linux. Even lets you remotely control mouse and keyboard! This free service is a side project from the creators of Screencast-O-Matic.com and is still in BETA. We use it extensively for remote user support and collaboration. The current version creates a direct peer-to-peer connection, so if you're on a super duper secure school or company network it may or may not be able to connect, but in most cases you'll find it works quite well so give it a shot!