The Collaborative International Dictionary of English v.0.48:

Blameless \Blame"less\, a.
   Free from blame; without fault; innocent; guiltless; --
   sometimes followed by of.
   [1913 Webster]

         A bishop then must be blameless.         --1 Tim. iii.
                                                  2.
   [1913 Webster]

         Blameless still of arts that polish to deprave.
                                                  --Mallet.
   [1913 Webster]

         We will be blameless of this thine oath. --Josh. ii.
                                                  17.
   [1913 Webster]

   Syn: Irreproachable; sinless; unblemished; inculpable.

   Usage: Blameless, Spotless, Faultless, Stainless. We
          speak of a thing as blameless when it is free from
          blame, or the just imputation of fault; as, a
          blameless life or character. The others are stronger.
          We speak of a thing as faultless, stainless, or
          spotless, only when we mean that it is absolutely
          without fault or blemish; as, a spotless or stainless
          reputation; a faultless course of conduct. The last
          three words apply only to the general character, while
          blameless may be used in reverence to particular
          points; as, in this transaction he was wholly
          blameless. We also apply faultless to personal
          appearance; as, a faultless figure; which can not be
          done in respect to any of the other words.
          [1913 Webster]

WordNet (r) 3.0 (2006):

blameless
    adj 1: free of guilt; not subject to blame; "has lived a
           blameless life"; "of irreproachable character"; "an
           unimpeachable reputation" [syn: blameless,
           inculpable, irreproachable, unimpeachable]

Moby Thesaurus II by Grady Ward, 1.0:

82 Moby Thesaurus words for "blameless":
   Christian, angelic, childlike, clean, clear, creditable, decent,
   dovelike, erect, estimable, ethical, exemplary, fair, faultless,
   full of integrity, good, guiltless, high-minded, high-principled,
   highly respectable, honest, honorable, immaculate, in the clear,
   incorrupt, inculpable, innocent, inviolate, irreprehensible,
   irreproachable, just, lamblike, law-abiding, law-loving,
   law-revering, lily-white, manly, moral, noble, not guilty,
   offenseless, prelapsarian, principled, pristine, pure,
   reproachless, reputable, respectable, right, right-minded,
   righteous, sans reproche, sinless, spotless, stainless, sterling,
   true-dealing, true-devoted, true-disposing, true-souled,
   true-spirited, truehearted, unblemished, uncorrupt, uncorrupted,
   undefiled, unfallen, unimpeachable, unlapsed, unspotted, unstained,
   unsullied, untarnished, untouched by evil, upright, uprighteous,
   upstanding, virtuous, with clean hands, without reproach, worthy,
   yeomanly