I'm going to try to do this in alphabetical order, to the best of my ability. I'm listing people by their twitter handle, because otherwise I get confused. I'll be updating this list silently. It is current to 8/29/2010.
Some people were drafted (like PZMyers) and some people volunteers.
All that's necessary to be part of the ScienceMob is a demonstrated ability to confront and refute proponents of pseudoscience. Some people do this primarily on Twitter; others on their blog or elsewhere.