WordNet (r) 3.0 (2006):

go to bed
    v 1: prepare for sleep; "I usually turn in at midnight"; "He
         goes to bed at the crack of dawn" [syn: go to bed, turn
         in, bed, crawl in, kip down, hit the hay, hit the
         sack, sack out, go to sleep, retire] [ant: arise,
         get up, rise, turn out, uprise]

Moby Thesaurus II by Grady Ward, 1.0:

19 Moby Thesaurus words for "go to bed":
   bed, bed down, couch, curl up, go beddy-bye, go night-night,
   go to rest, lie down, loll, lounge, recline, repose, rest, retire,
   settle to rest, snug down, sprawl, take it easy, take life easy