WordNet (r) 3.0 (2006):

long ago
    adv 1: of the distant or comparatively distant past; "We met
           once long ago"; "they long ago forsook their nomadic
           life"; "left for work long ago"; "he has long since given
           up mountain climbing"; "This name has long since been
           forgotten"; "lang syne" is Scottish [syn: long ago,
           long since, lang syne]

Moby Thesaurus II by Grady Ward, 1.0:

53 Moby Thesaurus words for "long ago":
   ages ago, anciently, and night, auld lang syne, away back,
   day after day, days beyond recall, days of old, days of yore,
   early, early times, eld, enduringly, for an age, for life,
   for long, good old times, hour after hour, in ancient times,
   in olden times, in times past, interminably, lang syne, long,
   long since, month after month, morning, noon, of old, of yore,
   old days, old story, old times, olden times, persistently,
   protractedly, same old story, since time began, some time ago,
   some time back, the livelong day, the olden time, till doomsday,
   time immemorial, times of old, times of yore, undyingly,
   unendingly, way back, year after year, years ago, yore, yoretime