The Collaborative International Dictionary of English v.0.48:

Attentive \At*ten"tive\ ([a^]t*t[e^]n"t[i^]v), a. [Cf. F.
   attentif.]
   1. Heedful; intent; observant; regarding with care or
      attention.
      [1913 Webster]

   Note: Attentive is applied to the senses of hearing and
         seeing, as, an attentive ear or eye; to the application
         of the mind, as in contemplation; or to the application
         of the mind, in every possible sense, as when a person
         is attentive to the words, and to the manner and
         matter, of a speaker at the same time.
         [1913 Webster]

   2. Heedful of the comfort of others; courteous.
      [1913 Webster]

   Syn: Heedful; intent; observant; mindful; regardful;
        circumspect; watchful.
        [1913 Webster] -- At*ten"tive*ly, adv. --
        At*ten"tive*ness, n.
        [1913 Webster]

WordNet (r) 3.0 (2006):

attentive
    adj 1: (often followed by `to') giving care or attention;
           "attentive to details"; "the nurse was attentive to her
           patient"; "an attentive suitor" [ant: inattentive]
    2: taking heed; giving close and thoughtful attention; "heedful
       of the warnings"; "so heedful a writer"; "heedful of what
       they were doing" [syn: heedful, attentive, thoughtful,
       paying attention] [ant: heedless, unheeding]

Moby Thesaurus II by Grady Ward, 1.0:

129 Moby Thesaurus words for "attentive":
   accommodating, accommodative, accurate, advertent, affable, agile,
   agog, agreeable, alert, alive, all ears, all eyes, assiduous,
   attenuate, awake, aware, bright, cap in hand, careful, cautious,
   ceremonious, circumspect, civil, close, complaisant, concentrated,
   concentrating, conscientious, conscious, considerate, correct,
   courteous, courtly, critical, curious, deferential, delicate,
   demanding, detailed, diligent, dutiful, eager, earnest, exact,
   exacting, exigent, exquisite, fair, fine, finical, finicking,
   finicky, fussy, gallant, graceful, gracious, heedful, helpful,
   honorific, indulgent, intense, intent, intentive, interested, keen,
   lenient, listening, loving, meticulous, mindful, mindful of others,
   minute, narrow, nice, niggling, nimble, obliging, observant,
   observing, on the, on the alert, on the ball, on the job,
   open-eared, open-eyed, openmouthed, particular, polite, precise,
   precisianistic, precisionistic, prompt, punctilious, punctual,
   qui vive, quick, ready, reedy, refined, regardful, religious,
   respectful, rigid, rigorous, scrupulous, scrutinizing, sharp,
   sleepless, slender, slight, slim, smart, solicitous, strict,
   subtle, tactful, tender, tenuous, thoughtful, tolerant, twiggy,
   unblinking, unnodding, unsleeping, unwinking, urbane, wakeful,
   watchful, wide-awake