Mister Thread is a new (beta) site that is one of many for creating a back channel chat. It is very easy to do an creates a unique URL (that you can password protect) to share w/ others who want to invite into your chat. What makes this a nice site to use is that no registration is required.
Click here to give MisterThread a try!!
Thanks to Larry Ferlazzo's blog for the tip!!
For my list of top 10 Back Channel Chat sites click here.