The Collaborative International Dictionary of English v.0.48:

Memorable \Mem"o*ra*ble\, a. [L. memorabilis, fr. memorare to
   bring to remembrance, fr. memor mindful, remembering. See
   Memory, and cf. Memorabilia.]
   Worthy to be remembered; very important or remarkable. --
   Mem"o*ra*ble*ness, n. -- Mem"o*ra*bly, adv.
   [1913 Webster]

         Surviving fame to gain,
         Buy tombs, by books, by memorable deeds. --Sir J.
                                                  Davies.
   [1913 Webster]

WordNet (r) 3.0 (2006):

memorable
    adj 1: worth remembering

Moby Thesaurus II by Grady Ward, 1.0:

40 Moby Thesaurus words for "memorable":
   catchy, celebrated, conspicuous, deathless, distinguished, eminent,
   esteemed, estimable, eventful, exceptional, extraordinary, great,
   historic, illustrious, important, marked, momentous, noble,
   notable, noteworthy, observable, of mark, outstanding, prestigious,
   prominent, rare, recollectable, red-letter, remarkable,
   rememberable, reputable, rubric, salient, signal, significant,
   special, striking, telling, unforgettable, worthy