WordNet (r) 3.0 (2006):

fair to middling
    adj 1: about average; acceptable; "more than adequate as a
           secretary" [syn: adequate, passable, fair to
           middling, tolerable]

Moby Thesaurus II by Grady Ward, 1.0:

23 Moby Thesaurus words for "fair to middling":
   betwixt and between, dull, fair, fairish, indifferent, insipid,
   lackluster, mediocre, medium, middling, moderate, modest,
   namby-pamby, of a kind, of a sort, of sorts, passable, respectable,
   so-so, tedious, tolerable, vapid, wishy-washy