I had this in the straw poll thread, but since that one is getting crazy long, here's a new overflow thread.
Here's the official difference between a "fantasy" candidate and a real one, at this point --
While no one has officially announced their candidacy, and won't until 2007, every name on the list above has a leadership PAC or is currently running a campaign -- hence they are staffing up their political operation. Fantasy candidates do not have a political operation working for them.
Their respective political operations: