WordNet (r) 3.0 (2006):

ombudsman
    n 1: a government appointee who investigates complaints by
         private persons against the government

Moby Thesaurus II by Grady Ward, 1.0:

50 Moby Thesaurus words for "ombudsman":
   JA, agent, amicus curiae, assessor, barmaster, chancellor,
   circuit judge, connection, deputy, front, front man, go-between,
   interagent, interceder, intercessor, intermediary, intermediate,
   intermediate agent, intermediator, intermedium, internuncio,
   intervener, interventionist, interventor, judge advocate,
   judge ordinary, jurat, justice in eyre, justice of assize,
   lay judge, legal assessor, master, mediator, medium, middleman,
   military judge, mouthpiece, negotiant, negotiator, negotiatress,
   negotiatrix, ordinary, police judge, presiding judge,
   probate judge, puisne judge, recorder, spokesman, spokeswoman,
   vice-chancellor