WordNet (r) 3.0 (2006):

out of sight
    adv 1: no longer visible; "the ship disappeared behind the
           horizon and passed out of sight" [syn: out of sight,
           out of view]
    2: quietly in concealment; "he lay doggo" [syn: doggo, out of
       sight, in hiding]
    adj 1: not accessible to view; "concealed (or hidden) damage";
           "in stormy weather the stars are out of sight" [syn:
           concealed, hidden, out of sight]

Moby Thesaurus II by Grady Ward, 1.0:

164 Moby Thesaurus words for "out of sight":
   OK, a bit much, abandoned, absconded, absent, ace-high, afar,
   afar off, away, bad, bang-up, behind the curtain,
   behind the scenes, beyond reach, beyond the bounds, bonzer, boss,
   boundless, bully, but good, camouflaged, concealed, cool, corking,
   crackerjack, cutthroat, dandy, deleted, delicious, departed,
   disappeared, disguised, ducky, egregious, enormous, exacting,
   exaggerated, excessive, exorbitant, extinct, extortionate,
   extravagant, extreme, fab, fabulous, fancy, far, far away, far off,
   fine and dandy, gear, gigantic, gluttonous, gone, gone away, goody,
   gouging, great, groovy, grossly overpriced, heavy, hidden, high,
   hot, hunky-dory, hyperbolic, hypertrophied, immoderate,
   imperceptible, incontinent, indiscernible, inflationary,
   inordinate, insensible, intemperate, invisible, jam-up, just dandy,
   keen, lacking, latent, lost, lost to sight, lost to view, marvy,
   mean, missing, monstrous, neat, nifty, no longer present, no more,
   nobby, nonattendant, nonexistent, not found, not present, okay,
   omitted, out of bounds, out of earshot, out of hearing,
   out of range, out of reach, outrageous, overbig, overdeveloped,
   overgreat, overgrown, overlarge, overmuch, overpriced, overweening,
   past and gone, peachy, peachy-keen, preposterous, prohibitive,
   ripping, rum, scrumptious, secret, sightless, skyrocketing,
   slap-up, smashing, solid, something else, spiffing, spiffy,
   spiraling, steep, stiff, stunning, submerged, subtracted, swell,
   taken away, too much, tough, unapparent, unbeheld, unbeholdable,
   unbridled, unconscionable, undiscernible, undue, unnoticed,
   unobserved, unperceivable, unperceived, unrealized, unreasonable,
   unrestrained, unseeable, unseen, unviewed, unwarranted,
   unwitnessed, usurious, vanished, viewless, wanting, wizard