2cb, 2ce, 2ci, foxy, bzp/tmfpp, bromo dragonfly, 5meodmt, 4hodipt, real-god-damn-actual-ayahuasca-with-a-shaman. LSD and pure MDMA(molly), although i'd hardly consider them rare. GHB, GBL, BDO, Ketamine, do those count?
the fact that we've all done these RC's(especially me, a non-scene, non-raver, relatively timid drug user) makes me feel like they must not be all that rare.