The Collaborative International Dictionary of English v.0.48:

out-of-sight \out-of-sight\ adj.
   very good; same as groovy, sense 1. [informal, 1960's]

   Syn: bang-up, bully, cool, corking, cracking, dandy, far-out,
        great, groovy, keen, neat, nifty, not bad(predicate),
        outtasight, peachy, psychedelic, slap-up, swell,
        smashing.
        [PJC]