The Collaborative International Dictionary of English v.0.48:

Insatiable \In*sa"tia*ble\, a. [F. insatiable, L. ionsatiabilis.
   See In- not, and Satiable.]
   Not satiable; incapable of being satisfied or appeased; very
   greedy; as, an insatiable appetite, thirst, or desire.
   [1913 Webster]

         "Insatiable of glory."                   --Milton.
   [1913 Webster]

WordNet (r) 3.0 (2006):

insatiable
    adj 1: impossible to satisfy; "an insatiate appetite"; "an
           insatiable demand for old buildings to restore"; "his
           passion for work was unsatiable" [syn: insatiate,
           insatiable, unsatiable] [ant: satiate, satiated]

Moby Thesaurus II by Grady Ward, 1.0:

68 Moby Thesaurus words for "insatiable":
   Apician, a hog for, acquisitive, all-devouring, avaricious, avid,
   bolting, bottomless, clamorous, coveting, covetous, cramming,
   crapulent, crapulous, crying, demanding, devouring, edacious,
   esurient, exigent, glutting, gluttonizing, gluttonous, gobbling,
   gorging, grabby, grasping, greedy, gulping, guttling, guzzling,
   hoggish, hyperphagic, importunate, insatiate, insistent,
   intemperate, limitless, mercenary, miserly, money-hungry,
   money-mad, omnivorous, overgreedy, piggish, polyphagic, pressing,
   quenchless, rapacious, ravening, ravenous, slakeless, sordid,
   stuffing, swinish, unappeasable, unappeased, unquenchable, unsated,
   unsatisfiable, unsatisfied, unslakeable, unslaked, urgent, venal,
   voracious, wolfing, yearning