The Collaborative International Dictionary of English v.0.48:

Despicable \Des"pi*ca*ble\, a. [L. despicabilis, fr. despicari
   to despise; akin to despicere. See Despise.]
   Fit or deserving to be despised; contemptible; mean; vile;
   worthless; as, a despicable man; despicable company; a
   despicable gift.

   Syn: Contemptible; mean; vile; worthless; pitiful; paltry;
        sordid; low; base. See Contemptible.
        [1913 Webster]

WordNet (r) 3.0 (2006):

despicable
    adj 1: morally reprehensible; "would do something as despicable
           as murder"; "ugly crimes"; "the vile development of
           slavery appalled them"; "a slimy little liar" [syn:
           despicable, ugly, vile, slimy, unworthy,
           worthless, wretched]

Moby Thesaurus II by Grady Ward, 1.0:

136 Moby Thesaurus words for "despicable":
   abhorrent, abject, abominable, arrant, atrocious, awful, base,
   beastly, beggarly, below contempt, beneath contempt, blameworthy,
   brutal, cheap, cheesy, common, contemptible, crude, crummy,
   debased, degraded, deplorable, depraved, detestable, dire, dirty,
   disgraceful, disgusting, disreputable, dreadful, egregious,
   enormous, execrable, fetid, filthy, flagrant, forbidding, foul,
   fulsome, gaudy, gimcracky, grave, grievous, gross, hateful,
   heinous, horrible, horrid, ignoble, ignominious, infamous,
   lamentable, little, loathsome, lousy, low, low-down, lumpen,
   malodorous, mangy, mean, measly, mephitic, meretricious, miasmal,
   miasmic, miserable, monstrous, nasty, nauseating, nefarious,
   noisome, notorious, noxious, objectionable, obnoxious, obscene,
   odious, offensive, outrageous, paltry, pathetic, petty, pitiable,
   pitiful, poky, poor, rank, rebarbative, regrettable, repellent,
   reprehensible, reptilian, repugnant, repulsive, revolting, rotten,
   rubbishy, sad, scabby, scandalous, schlock, scrubby, scruffy,
   scummy, scurvy, scuzzy, shabby, shameful, shameless, shocking,
   shoddy, sickening, small, sordid, sorry, squalid, stinking,
   terrible, too bad, trashy, trumpery, two-for-a-cent,
   two-for-a-penny, twopenny, twopenny-halfpenny, ugly, unclean,
   unmentionable, valueless, vile, villainous, woeful, worst,
   worthless, wretched