The Collaborative International Dictionary of English v.0.48:

Flatterer \Flat"ter*er\, n.
   One who flatters.
   [1913 Webster]

         The most abject flaterers degenerate into the greatest
         tyrants.                                 --Addison.
   [1913 Webster]

WordNet (r) 3.0 (2006):

flatterer
    n 1: a person who uses flattery [syn: flatterer, adulator]

Moby Thesaurus II by Grady Ward, 1.0:

51 Moby Thesaurus words for "flatterer":
   adulator, apple-polisher, ass-licker, backscratcher, backslapper,
   blarneyer, bootlick, bootlicker, brown-nose, brownie, cajoler,
   clawback, courtier, creature, cringer, dupe, fawner, flunky,
   footlicker, groveler, handshaker, hanger-on, helot, instrument,
   jackal, kowtower, lackey, led captain, leech, lickspit,
   lickspittle, mealymouth, minion, parasite, peon, puppet, serf,
   slave, spaniel, sponge, stooge, suck, sycophant, timeserver, toad,
   toady, tool, truckler, tufthunter, wheedler, yes-man