Couchmate - Chat about live TV, together!
Metastream - Watch streaming media with friends
histre - Smart Bookmarks, with With Notes, Highlights, History, and Sharing
Watch2Gether - Watch2Gether is an app that allows multiple people to watch the same content simultaneously and interact with each other while watching.
Invited.tv - Watch together from anywhere and hang out with friends online
Hyperbeam - A better way to watch together online