WordNet (r) 3.0 (2006):

unconscientious
    adj 1: not conscientious; [ant: conscientious]

Moby Thesaurus II by Grady Ward, 1.0:

55 Moby Thesaurus words for "unconscientious":
   amoral, conscienceless, corrupt, corrupted, criminal, crooked,
   dark, devious, dishonest, dishonorable, doubtful, dubious, evasive,
   felonious, fishy, fraudulent, ill-got, ill-gotten, immoral,
   inaccurate, indirect, inexact, insidious, not kosher, questionable,
   rotten, shady, shameless, shifty, sinister, slippery, suspicious,
   tricky, unconscienced, unconscionable, uncritical, underhand,
   underhanded, unethical, unexacting, unfinical, unfussy,
   unmeticulous, unpainstaking, unparticular, unprecise, unprincipled,
   unpunctilious, unpunctual, unrigorous, unsavory, unscrupulous,
   unstraightforward, without remorse, without shame