Great thread! Its always been a hobby of mine to search out those "off the beaten track" recordings that seem all but lost majority if listeners. I used to be particularly fond of looking for b-sides to whatever band I was into and it was such a treat to finally stumble on that rare single ep backed with some obscure song you'd always heard about but never actually listened too.
Anyway I thought I might add an old favorite of mine to the list.
John Coltrane "OM"
Recorded in October of 1965 this, now rare, album offers a shocking glimpse into Coltrane's descent into free jazz madness. Released posthumously, and unlike similar recordings from this era (A Love Supreme, Ascension) it was universally panned by fans and critics alike before seemingly disappearing from the Impulse! catalogue by the late 80's (Checking around a few minutes ago online I did find a few used/import copies selling for $50 and up, nothing on itunes). In recent years this recording seems to have made a bit of a comeback amongst jazz fans and despite an almost endless amount of unreleased/reissued Coltrane material "Om" still seemingly hasn't seen the light of day. Incidentally rumor has it this recording and the bootleg "Live in Seattle" recorded the previous night were the results of an apparently very long acid trip that Coltrane HAD to get on tape, although most people seem to regard that as urban legend.
Below is an excerpt of the (in)famous John Coltrane, Pharoah Sanders solo duel from "Om" ...enjoy...