The Collaborative International Dictionary of English v.0.48:

Excitable \Ex*cit"a*ble\, a. [L. excitabilis inciting: cf. F.
   excitable.]
   Capable of being excited, or roused into action; susceptible
   of excitement; easily stirred up, or stimulated.
   [1913 Webster]

WordNet (r) 3.0 (2006):

excitable
    adj 1: easily excited [ant: unexcitable]
    2: capable of responding to stimuli [syn: excitable,
       irritable]

Moby Thesaurus II by Grady Ward, 1.0:

72 Moby Thesaurus words for "excitable":
   agitable, all nerves, apprehensive, bearish, bitchy, cankered,
   cantankerous, churlish, combustible, crabbed, cranky, cross,
   cross-grained, crusty, cussed, disagreeable, edgy, emotional,
   emotionally unstable, eruptive, explosive, fearful, feisty,
   feverish, fidgety, fractious, frightened, high-mettled,
   high-spirited, high-strung, highly emotional, hot-blooded, huffish,
   huffy, hysterical, inflammable, irascible, irritable, jumpy, mean,
   mercurial, mettlesome, nerves on edge, nervous, nervy, on edge,
   ornery, overstrung, panicky, perturbable, perverse, prickly,
   quick-tempered, restive, restless, sensitive, skittery, skittish,
   snappish, spiteful, spleeny, splenetic, startlish, temperamental,
   testy, touchy, ugly, uneasy, unstable, volatile, volcanic,
   waspish