WordNet (r) 3.0 (2006):

public speaker
    n 1: a person who delivers a speech or oration [syn: orator,
         speechmaker, rhetorician, public speaker,
         speechifier]

Moby Thesaurus II by Grady Ward, 1.0:

30 Moby Thesaurus words for "public speaker":
   Cicero, Demosthenes, William Jennings Bryan, Winston Churchill,
   debater, declaimer, demagogue, haranguer, jawsmith, orator,
   panelist, platform orator, rabble-rouser, ranter, rhetor,
   rhetorician, soapbox orator, soapboxer, speaker, speecher,
   speechifier, speechmaker, spellbinder, spieler, spokesman,
   spokeswoman, spouter, stump orator, talker, tub-thumper