As I mentioned before, Skype is a tool with great potential for your classroom. It provides the chance for connection, be it with another classroom or a professional in the field. And it is free.
I used to participate in the iSighted.com community when it was in existence. iSighted was a group of people who made themselves available for videoconferencing, putting their names in a directory for searching.
Now, there is a new service called Skype in Schools. Not only can you check for people to connect with for your classroom's project, but you can also make yourself available.
Tip of the hat to Dr. Z at UNI, who mentioned the service in his last blog. Both he and I are available there.