The Collaborative International Dictionary of English v.0.48:

Stimulate \Stim"u*late\, v. t. [imp. & p. p. Stimulated; p.
   pr. & vb. n. Stimulating.] [L. stimulatus, p. p. of
   stimulare to prick or goad on, to incite, fr. stimulus a
   goad. See Stimulus.]
   1. To excite as if with a goad; to excite, rouse, or animate,
      to action or more vigorous exertion by some pungent motive
      or by persuasion; as, to stimulate one by the hope of
      reward, or by the prospect of glory.
      [1913 Webster]

            To excite and stimulate us thereunto. --Dr. J.
                                                  Scott.
      [1913 Webster]

   2. (Physiol.) To excite; to irritate; especially, to excite
      the activity of (a nerve or an irritable muscle), as by
      electricity.
      [1913 Webster]

   Syn: To animate; incite; encourage; impel; urge; instigate;
        irritate; exasperate; incense.
        [1913 Webster]

WordNet (r) 3.0 (2006):

stimulating
    adj 1: rousing or quickening activity or the senses; "a
           stimulating discussion" [ant: unexciting,
           unstimulating]
    2: that stimulates; "stimulant phenomena" [syn: stimulant,
       stimulating]
    3: making lively and cheerful; "the exhilarating effect of
       mountain air" [syn: exhilarating, stimulating]

Moby Thesaurus II by Grady Ward, 1.0:

122 Moby Thesaurus words for "stimulating":
   activating, agitating, alluring, analeptic, animating, animative,
   aphrodisiac, aphroditous, ardent, arousing, bracing, breathtaking,
   brisk, burning, challenging, charged, cheering, chill, chilly,
   cliff-hanging, cool, coolish, cordial, corroborant, crisp, crispy,
   disquieting, distracting, disturbing, electric, emphatic,
   encouraging, energizing, enlivening, enthusiastic, eroticizing,
   exciting, exhilarating, exhilarative, fervent, fiery, fresh,
   galvanic, galvanizing, glowing, heady, heart-expanding,
   heart-stirring, heart-swelling, heart-thrilling, impassioned,
   impressive, inflammatory, inspirational, inspiring, interesting,
   intoxicating, invigorating, invigorative, inviting, jarring,
   jolting, juicy, lively, maddening, mind-blowing, moving,
   overcoming, overmastering, overpowering, overwhelming, passionate,
   perturbing, piquant, prompting, provocative, provoking, quickening,
   racy, ravishing, readable, refreshful, refreshing, regaling,
   restorative, reviving, rich, roborant, rousing, soul-stirring,
   spicy, spirit-stirring, stimulant, stimulative, stirring,
   strengthening, striking, succulent, suspenseful, suspensive,
   tantalizing, telling, temperate, thought-challenging,
   thought-inspiring, thought-provoking, thrilling, thrilly, tickling,
   titillating, tonic, troubling, unsettling, upsetting, urgent,
   vehement, venereal, viable, vitalizing, warm, zestful, zesty