Watch2gether is a great site for watching YouTube videos w/ others. This site allows users to discuss YouTube videos via a text chat that opens up on the right side of the window.
Celly is a wonderful free site for using mobile phones/text messaging in the classroom (found out about from a member of my PLN on Twitter). There is a lot to like about using Celly such as: creating a chat, alerting, and even using a curator to approve messages before they get posted (ideal for education). Also, it's ideal for taking notes, interacting w/ web (no phone is actually needed), etc etc.