The USMC has the overwhelming majority of Harriers, although, if I'm not mistaken NASA maintains(-ed?) a limited # for testbed purposes.
jettester, do you have any more info on Harriers procured by agencies other than the USMC?
The B II+ models were also purchased by the Spanish and Italian fleets because it allowed for a better integration into the NATO spec weaponry and electronics. Those two and our beloved jarheads were the only other publicly announced sales of these birds.