WordNet (r) 3.0 (2006):

like clockwork
    adv 1: with regularity and precision; "the rocket launch went
           off like clockwork"

Moby Thesaurus II by Grady Ward, 1.0:

34 Moby Thesaurus words for "like clockwork":
   always, at every turn, at regular intervals, at stated times,
   constantly, continually, easily, effortlessly, evenly,
   every so often, facilely, hands down, harmoniously, intermittently,
   invariably, lightly, like nothing, methodically, never otherwise,
   no sweat, on easy terms, on wheels, orderly, punctually, readily,
   regularly, simply, smoothly, steadily, swimmingly, systematically,
   uniformly, without difficulty, without exception