Perhaps the thing I admire most about A.G. Lafley, who recently stepped down after running Procter & Gamble for a decade, is that, in contrast to so many other CEOs, he doesn't pretend for a second that he discovered a new way to manage, or that his success resulted from any mysterious and complicated methods.
This is the traffic cop of the session, and should be an outsider. An insider brings baggage that can inhibit the free flow of ideas. HR consulting organizations are one possible resource; if you are working with a design firm like IDEO or Continuum, they may be able to help. If bringing in an outsider is difficult for some reason, the second best option is to bring in someone from a different group inside the company. Facilitators need to be skilled at group dynamics, able to read when the team is flagging or when it is hitting on all cylinders.