The Collaborative International Dictionary of English v.0.48:

Blissful \Bliss"ful\, a.
   Full of, characterized by, or causing, joy and felicity;
   happy in the highest degree. "Blissful solitude." --Milton.
   -- Bliss"ful*ly, adv. -- Bliss"ful*ness, n.
   [1913 Webster]

WordNet (r) 3.0 (2006):

blissful
    adj 1: completely happy and contented; "blissful young lovers";
           "in blissful ignorance"

Moby Thesaurus II by Grady Ward, 1.0:

75 Moby Thesaurus words for "blissful":
   Elysian, affable, agreeable, amiable, amicable, beaming, beatific,
   beatified, blessed, capering, cheerful, chirping, compatible,
   complaisant, congenial, cordial, dancing, desirable, divine,
   dulcet, empyreal, empyrean, en rapport, enjoyable, fair,
   fair and pleasant, felicific, felicitous, fine, flushed with joy,
   gay, genial, glad, glowing, good, goodly, gracious, grateful,
   gratifying, happy, harmonious, heart-warming, heavenly, honeyed,
   joyful, joyous, laughing, leaping, likable, mellifluous, mellow,
   nice, paradisiac, paradisial, paradisian, paradisic, pleasant,
   pleasing, pleasurable, pleasure-giving, pleasureful, purring,
   radiant, rewarding, saintly, satisfying, singing, smiling,
   smirking, sparkling, starry-eyed, sublime, sweet, thrice happy,
   welcome