The Collaborative International Dictionary of English v.0.48:

motivated \motivated\ adj.
   Having a strong motive; -- of people. Opposite of
   unmotivated. [Narrower terms: driven, impelled]
   [WordNet 1.5] motivating

WordNet (r) 3.0 (2006):

motivated
    adj 1: provided with a motive or given incentive for action; "a
           highly motivated child can learn almost anything"; "a
           group of politically motivated men" [ant: unmotivated]

Moby Thesaurus II by Grady Ward, 1.0:

34 Moby Thesaurus words for "motivated":
   actuated, animated, apt, bright, clever, docile, educable, facile,
   formable, impelled, impressionable, inclined, inner-directed,
   instructable, intelligent, malleable, minded, moldable, moved,
   other-directed, plastic, pliable, prompted, quick, ready,
   receptive, ripe for instruction, schoolable, stimulated,
   susceptible, teachable, thirsty for knowledge, trainable,
   willing