WordNet (r) 3.0 (2006):

high horse
    n 1: an attitude of arrogant superiority; "get off your high
         horse and admit you are wrong"

Moby Thesaurus II by Grady Ward, 1.0:

30 Moby Thesaurus words for "high horse":
   Olympian detachment, Olympian loftiness, arrogance, arrogantness,
   assumption of superiority, condescendence, condescension,
   domineering, domineeringness, haughtiness, haughty airs, hauteur,
   hoity-toitiness, hoity-toity, loftiness, overbearing pride,
   overbearingness, overweening pride, patronization, patronizing,
   patronizing attitude, pride, proudness, purse-pride, side,
   stiff-necked pride, superbia, toploftiness, uppishness,
   uppityness