The Collaborative International Dictionary of English v.0.48:

Prevalent \Prev"a*lent\, a. [L. praevalens, -entis, p. pr. of
   praevalere. See Prevail.]
   1. Gaining advantage or superiority; having superior force,
      influence, or efficacy; prevailing; predominant;
      successful; victorious.
      [1913 Webster]

            Brennus told the Roman embassadors, that prevalent
            arms were as good as any title.       --Sir W.
                                                  Raleigh.
      [1913 Webster]

   2. Most generally received or current; most widely adopted or
      practiced; also, generally or extensively existing;
      widespread; prevailing; as, a prevalent observance;
      prevalent disease.
      [1913 Webster]

            This was the most received and prevalent opinion.
                                                  --Woodward.
      [1913 Webster]

   Syn: Prevailing; predominant; successful; efficacious;
        powerful.

   Usage: Prevalent, Prevailing. What customarily prevails
          is prevalent; as, a prevalent fashion. What actually
          prevails is prevailing; as, the prevailing winds are
          west. Hence, prevailing is the livelier and more
          pointed word, since it represents a thing in action.
          It is sometimes the stronger word, since a thing may
          prevail sufficiently to be called prevalent, and yet
          require greater strength to make it actually
          prevailing.
          [1913 Webster]

WordNet (r) 3.0 (2006):

prevalent
    adj 1: most frequent or common; "prevailing winds" [syn:
           prevailing, prevalent, predominant, dominant,
           rife]

Moby Thesaurus II by Grady Ward, 1.0:

194 Moby Thesaurus words for "prevalent":
   abounding, abundant, accepted, accidental, accompanying, ado,
   affluent, afloat, afoot, all the rage, all the thing,
   all-sufficing, ample, aplenty, ascendant, at the head, average,
   being, besetting, boss, bottomless, bounteous, bountiful, catholic,
   chief, circumstantial, commanding, common, commonplace,
   conformable, consuetudinary, controlling, conventional, copious,
   current, customary, diffuse, doing, dominant, effuse, epidemic,
   established, eventuating, everyday, exhaustless, existent,
   existing, extant, extensive, extravagant, exuberant, familiar,
   fashionable, fat, fertile, flush, frequent, frequentative, full,
   galore, general, generally accepted, generous, going on, governing,
   habitual, happening, head, hegemonic, hegemonistic, hip,
   in ascendancy, in being, in charge, in chief, in effect,
   in existence, in fashion, in force, in hand, in plenty,
   in quantity, in style, in the ascendant, in the wind, in vogue,
   incidental, inexhaustible, lavish, leading, liberal, living,
   luxuriant, many, many times, master, maximal, mod, modern, much,
   new, newfashioned, normal, not rare, numerous, obtaining,
   occasional, occurring, of common occurrence, oft-repeated,
   oftentime, omnipresent, on, on foot, ongoing, opulent, ordinary,
   overbearing, overflowing, pandemic, paramount, passing, pervasive,
   plenitudinous, plenteous, plentiful, plenty, popular, predominant,
   predominate, predominating, prepollent, preponderant, preponderate,
   prepotent, prescribed, prescriptive, present, prevailing, prodigal,
   productive, profuse, profusive, rampant, received, recurrent,
   regnant, regular, regulating, regulation, regulative, regulatory,
   reigning, replete, resultant, rich, rife, riotous, routine, ruling,
   running, running over, set, smart, sovereign, standard,
   stereotyped, stock, subsistent, subsisting, superabundant, supreme,
   taking place, teeming, thick-coming, time-honored, traditional,
   trendy, ubiquitous, under the sun, under way, universal,
   up-to-date, up-to-datish, up-to-the-minute, usual, wealthy,
   well-found, well-furnished, well-provided, well-stocked, wholesale,
   widespread, wonted