The Collaborative International Dictionary of English v.0.48:

pacesetter \pacesetter\ n.
   A horse used to set the pace in racing.

   Syn: pacer, pacemaker.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

pacesetter
    n 1: a leading instance in its field; "the new policy will be a
         pacesetter in community relations" [syn: pacesetter,
         pacemaker]
    2: a horse used to set the pace in racing [syn: pacer,
       pacemaker, pacesetter]

Moby Thesaurus II by Grady Ward, 1.0:

24 Moby Thesaurus words for "pacesetter":
   Mahdi, bell cow, bell mare, bellwether, born leader,
   charismatic leader, choirmaster, choragus, conductor, coryphaeus,
   duce, file leader, forerunner, fugleman, inspired leader, leader,
   leader of men, messiah, pacemaker, precentor, ringleader,
   standard-bearer, symphonic conductor, torchbearer