The Collaborative International Dictionary of English v.0.48:

Cheerfully \Cheer"ful*ly\, adv.
   In a cheerful manner, gladly.
   [1913 Webster]

WordNet (r) 3.0 (2006):

cheerfully
    adv 1: in a cheerful manner; "he cheerfully agreed to do it"
           [ant: cheerlessly]

Moby Thesaurus II by Grady Ward, 1.0:

34 Moby Thesaurus words for "cheerfully":
   affably, agreeably, airily, amiably, amicably, blissfully,
   blithely, cheerily, confidently, cordially, enjoyably, expectantly,
   fair, fondly, genially, gladly, graciously, gratifyingly, happily,
   hopefully, hopingly, irrepressibly, jauntily, joyfully, kindly,
   lightly, optimistically, pleasantly, pleasingly, pleasurably,
   sanguinely, satisfyingly, smilingly, with good cheer



The Jargon File (version 4.4.7, 29 Dec 2003):

cheerfully
 adv.

    See happily.