WordNet (r) 3.0 (2006):

bonkers
    adj 1: informal or slang terms for mentally irregular; "it used
           to drive my husband balmy" [syn: balmy, barmy,
           bats, batty, bonkers, buggy, cracked,
           crackers, daft, dotty, fruity, haywire,
           kooky, kookie, loco, loony, loopy, nuts,
           nutty, round the bend, around the bend, wacky,
           whacky]

Moby Thesaurus II by Grady Ward, 1.0:

41 Moby Thesaurus words for "bonkers":
   balmy, bananas, barmy, bats, batty, beany, bedlamite, brainsick,
   buggy, bughouse, bugs, crackbrained, crackers, cuckoo, daffy,
   dippy, dotty, flaky, flipped, freaked-out, fruitcakey, fruity,
   gaga, goofy, haywire, just plain nuts, kooky, loony, loopy, nuts,
   nutty, off the hinges, off the track, off the wall, potty,
   round the bend, screwball, screwballs, screwy, slaphappy, wacky