Chat Rooms
TinyChat - With Tinychat, you can create your own chatroom and invite people through one simple link. You can also embed your chatroom on your blog, myspace, personal site, and many other portals. You can even invite people through email and twitter.
TodaysMeet - helps you embrace the backchannel and connect with your audience in realtime. Encourage the room to use the live stream to make comments, ask questions, and use that feedback to tailor your presentation, sharpen your points, and address audience needs.
Voxli - voice chat for everyone
Stinto - create you own chats in seconds and invite people to join by simply sending a short link.
Chatzy - a free private chat service which you can use to communicate with people you already know or people who visits your blog or website. With Chatzy you can create a chatroom and send out email invitations very quickly and easily. No registration is required.
backchan.nl is tool for involving audiences in presentations by letting them suggest questions and vote on each other's questions. backchan.nl is intended for conference or event organizers who want a new way to solicit questions from the audience and make better use of question and answer time
Google Moderator - Helping the world find the best input from an audience of any size.
Classroom ideas:
Back-channeling During a Class Viewing of Glory