The Collaborative International Dictionary of English v.0.48:

Opinionated \O*pin"ion*a`ted\, a.
   Stiff in opinion; firmly or unduly adhering to one's own
   opinion or to preconceived notions; obstinate in opinion.
   --Sir W. Scott.
   [1913 Webster]

WordNet (r) 3.0 (2006):

opinionated
    adj 1: obstinate in your opinions [syn: opinionated,
           opinionative, self-opinionated]

Moby Thesaurus II by Grady Ward, 1.0:

76 Moby Thesaurus words for "opinionated":
   antiblack, balking, balky, biased, bigoted, bulldogged,
   bulletheaded, bullheaded, case-hardened, chauvinistic, cocksure,
   colored, conceited, dictatorial, doctrinaire, doctrinarian, dogged,
   dogmatic, dogmatizing, fanatic, hardheaded, headstrong, inflexible,
   influenced, interested, intolerant, jaundiced, know-nothing,
   mulish, nonobjective, obdurate, obstinate, one-sided, opinionative,
   opinioned, oracular, overbearing, overzealous, partial, partisan,
   peremptory, persevering, pertinacious, pigheaded, pontifical,
   positive, positivistic, prejudiced, prepossessed, pronunciative,
   racist, restive, self-opinionated, self-opinioned, self-willed,
   set, sexist, single-minded, stiff-necked, strong-willed,
   strongheaded, stubborn, sulky, sullen, superpatriotic, swayed,
   tenacious, twisted, ultranationalist, uncooperative, undetached,
   undispassionate, unregenerate, warped, willful, xenophobic