The Collaborative International Dictionary of English v.0.48:

Pleasantness \Pleas"ant*ness\, n.
   The state or quality of being pleasant.
   [1913 Webster]

WordNet (r) 3.0 (2006):

pleasantness
    n 1: the feeling caused by agreeable stimuli; one pole of a
         continuum of states of feeling [ant: unpleasantness]
    2: the quality of giving pleasure; "he was charmed by the
       sweetness of her manner"; "the pleasantness of a cool breeze
       on a hot summer day" [syn: pleasantness, sweetness] [ant:
       unpleasantness]

Moby Thesaurus II by Grady Ward, 1.0:

64 Moby Thesaurus words for "pleasantness":
   advantageousness, agreeability, agreeableness, amiability,
   auspiciousness, beneficialness, benevolence, benignity, blitheness,
   blithesomeness, brightness, cheer, cheerfulness, cheeriness,
   cheery vein, class, cogency, cordiality, desert, enjoyableness,
   eupeptic mien, excellence, expedience, fairness, favorableness,
   fineness, first-rateness, geniality, gladness, gladsomeness,
   good cheer, goodliness, goodness, grace, gratefulness, happiness,
   healthiness, helpfulness, hopefulness, kindness, merit, niceness,
   optimism, pleasance, profitableness, quality, radiance,
   rewardingness, rosy expectation, sanguine humor, sanguineness,
   skillfulness, soundness, sunniness, superiority,
   sweetness and light, usefulness, validity, value, virtue,
   virtuousness, wholeness, winsomeness, worth