The Collaborative International Dictionary of English v.0.48:

Sermonizer \Ser"mon*i`zer\, n.
   One who sermonizes.
   [1913 Webster]

WordNet (r) 3.0 (2006):

sermonizer
    n 1: someone whose occupation is preaching the gospel [syn:
         preacher, preacher man, sermonizer, sermoniser]

Moby Thesaurus II by Grady Ward, 1.0:

26 Moby Thesaurus words for "sermonizer":
   Boanerges, chalk talker, churchman, circuit rider, cleric, clerk,
   discourser, divine, ecclesiastic, expositor, expounder, homilist,
   lecturer, minister, parson, praelector, preacher, preaching friar,
   predicant, predikant, pulpitarian, pulpiteer, pulpiter, reader,
   sermoner, sermonist