WordNet (r) 3.0 (2006):

spill the beans
    v 1: divulge confidential information or secrets; "Be careful--
         his secretary talks" [syn: spill the beans, let the cat
         out of the bag, talk, tattle, blab, peach,
         babble, sing, babble out, blab out] [ant: keep
         one's mouth shut, keep quiet, shut one's mouth]

Moby Thesaurus II by Grady Ward, 1.0:

29 Moby Thesaurus words for "spill the beans":
   babble, be indiscreet, be unguarded, betray, betray a confidence,
   blab, blabber, blurt, blurt out, give away, inform, inform on,
   leak, let drop, let fall, let slip, peach, rat, reveal a secret,
   sing, spill, squeal, stool, talk, tattle, tattle on, tell on,
   tell secrets, tell tales