HipChat is a site I've known about for quite sometime but decided to give it a look. This is a great site for creating a chat room. These rooms can be set to public or private, are very user friendly, and has a nice polished look to it. As w/ most chat rooms, people can send private messages to an individual user, attachments, and even do video and voice chatting.
I highly recommend checking out HipChat by clicking here!!
For a brief demo view below..
For my top 10 sites for creating a backchannel chat click here.