The Collaborative International Dictionary of English v.0.48:

Readable \Read"a*ble\ (r[=e]d"[.a]*b'l), a.
   Such as can be read; legible; fit or suitable to be read;
   worth reading; interesting. -- Read"a*ble*ness, n. --
   Read"a*bly, adv.
   [1913 Webster]

WordNet (r) 3.0 (2006):

readable
    adj 1: easily deciphered [syn: clear, decipherable,
           readable]

Moby Thesaurus II by Grady Ward, 1.0:

80 Moby Thesaurus words for "readable":
   absorbing, allegorical, apprehensible, articulate, associational,
   cognizable, comprehensible, connotational, connotative,
   decipherable, definable, denotational, denotative, distinct,
   easily understood, easy to understand, engaging, enjoyable,
   entertaining, exciting, exoteric, expressive, extended,
   extensional, fair, fathomable, figurative, full of meaning,
   full of point, full of substance, in the clear, indicative,
   intelligible, intensional, interesting, interpretable, inviting,
   juicy, knowable, legible, lively, meaning, meaningful, meaty,
   metaphorical, penetrable, piquant, pithy, plain, pleasurable,
   plumbable, pointed, pregnant, prehensible, provocative, provoking,
   racy, referential, rich, scrutable, sententious, significant,
   significative, spicy, stimulating, substantial, succulent,
   suggestive, symbolic, tantalizing, thought-challenging,
   thought-inspiring, thought-provoking, tickling, titillating,
   transferred, uncoded, understandable, unenciphered, worthwhile