WordNet (r) 3.0 (2006):

forever and a day
    adv 1: for a very long or seemingly endless time; "she took
           forever to write the paper"; "we had to wait forever and
           a day" [syn: forever, forever and a day]

Moby Thesaurus II by Grady Ward, 1.0:

39 Moby Thesaurus words for "forever and a day":
   and night, aye, day after day, enduringly, ever, ever and again,
   ever and anon, evermore, for all time, for an age, for aye,
   for good, for keeps, for life, for long, forever, forever and aye,
   forevermore, hour after hour, in all ages, interminably, long,
   long ago, long since, month after month, morning, noon,
   now and forever, persistently, protractedly, since time began,
   the livelong day, throughout the ages, till doomsday,
   till time stops, time immemorial, undyingly, unendingly,
   year after year