WordNet (r) 3.0 (2006):

long time
    n 1: a prolonged period of time; "we've known each other for
         ages"; "I haven't been there for years and years" [syn:
         long time, age, years]

Moby Thesaurus II by Grady Ward, 1.0:

28 Moby Thesaurus words for "long time":
   aeon, age, ages, century, distance, eternity, extension, extent,
   infinity, length, lengthiness, linear measures, long, long while,
   longitude, longness, measure, mileage, month of Sundays,
   overall length, perpetuity, reach, right smart spell, span,
   stretch, yardage, years, years on end