The Collaborative International Dictionary of English v.0.48:

Gladly \Glad"ly\, adv. [From Glad, a.]
   [1913 Webster]
   1. Preferably; by choice. [Obs.] --Chaucer.
      [1913 Webster]

   2. With pleasure; joyfully; cheerfully; eagerly.
      [1913 Webster]

            The common people heard him gladly.   --Mark xii.
                                                  37.
      [1913 Webster]

WordNet (r) 3.0 (2006):

gladly
    adv 1: in a willing manner; "this was gladly agreed to"; "I
           would fain do it" [syn: gladly, lief, fain]

Moby Thesaurus II by Grady Ward, 1.0:

27 Moby Thesaurus words for "gladly":
   airily, blessedly, blissfully, blithely, cheerfully, cheerily,
   delightedly, ecstatically, elatedly, exultantly, genially, happily,
   hopefully, irrepressibly, jauntily, joyfully, jubilantly, lightly,
   optimistically, pleasantly, rapturously, readily, rhapsodically,
   smilingly, willingly, with good cheer, with pleasure