The Collaborative International Dictionary of English v.0.48:

Grateful \Grate"ful\, a. [Grate, a. + full; cf. F. gr['e]
   thanks, good will, fr. L. gratum, neut. of gratus agreeable,
   grateful. See Grate, a.]
   1. Having a due sense of benefits received; kindly disposed
      toward one from whom a favor has been received; willing to
      acknowledge and repay, or give thanks for, benefits; as, a
      grateful heart.
      [1913 Webster]

            A grateful mind
            By owing, owes not, but still pays.   --Milton.
      [1913 Webster]

   2. Affording pleasure; pleasing to the senses; gratifying;
      delicious; as, a grateful present; food grateful to the
      palate; grateful sleep.
      [1913 Webster]

            Now golden fruits on loaded branches shine,
            And grateful clusters swell.          --Pope.

   Syn: Thankful; pleasing; acceptable; gratifying; agreeable;
        welcome; delightful; delicious. -- Grate"ful*ly, adv.
        -- Grate"ful*ness, n.
        [1913 Webster]

WordNet (r) 3.0 (2006):

grateful
    adj 1: feeling or showing gratitude; "a grateful heart";
           "grateful for the tree's shade"; "a thankful smile" [syn:
           grateful, thankful] [ant: thankless, ungrateful,
           unthankful]
    2: affording comfort or pleasure; "the grateful warmth of the
       fire"

Moby Thesaurus II by Grady Ward, 1.0:

64 Moby Thesaurus words for "grateful":
   acceptable, acknowledging, affable, agreeable, amiable, amicable,
   appreciative, beholden, blissful, cheerful, cognizant of,
   comforting, compatible, complaisant, congenial, consoling, cordial,
   crediting, delectable, delicious, delightful, desirable, dulcet,
   en rapport, enjoyable, fair, fair and pleasant, favorable,
   felicific, felicitous, fine, genial, good, goodly, gracious,
   gratified, gratifying, harmonious, heart-warming, honeyed,
   indebted to, likable, mellifluous, mellow, much obliged, nice,
   obliged, pleasant, pleased, pleasing, pleasurable, pleasure-giving,
   pleasureful, refreshing, rejuvenating, restorative, restoring,
   rewarding, satisfying, sensible, sweet, thankful, under obligation,
   welcome