The Collaborative International Dictionary of English v.0.48:

Perennially \Per*en"ni*al*ly\, adv.
   In a perennial manner.
   [1913 Webster]

WordNet (r) 3.0 (2006):

perennially
    adv 1: in a perennial manner; repeatedly; "We want to know what
           is perennially new about the world"

Moby Thesaurus II by Grady Ward, 1.0:

64 Moby Thesaurus words for "perennially":
   ad infinitum, again and again, always, at a stretch, at all times,
   ceaselessly, connectedly, constantly, continually, continuously,
   cumulatively, cyclically, daily, daily and hourly, day after day,
   day and night, endlessly, eternally, ever, ever and anon,
   everlastingly, every day, every hour, every moment,
   hour after hour, hourly, in perpetuity, incessantly,
   indestructibly, infinitely, interminably, monotonously,
   month after month, never-endingly, night and day, on a stretch,
   on and on, on end, perdurably, permanently, perpetually, rapidly,
   regularly, repetitively, right along, round the clock, steadily,
   sustainedly, time without end, together, unbrokenly, unceasingly,
   unendingly, unintermittently, uninterruptedly, unrelievedly,
   unvaryingly, without a break, without cease, without end,
   without letup, without stopping, world without end,
   year after year