Its hard as there was so much good stuff. There's got to be a record that is special to you, yet not necessarily mainstream. (Not looking for ABBA's greatest hits, not that there is anything wrong with that).
If I was stuck on a desert island (yeah, yeah there's no power on the island etc) that would be 'P.F's Dark Side of the Moon'.
But since the criteria is 'best yet obscure' record, my pick is Peter and the Wolf with Manfred Mann, Stephane Grappelli, Eno, Cozy Powell, Phil Collins et al. Background story - about 1975 was in a record store that has those booths with headphones to listen before you buy. Walked past a booth that had music coming from the headphones, put them on and though 'wow this is pretty awesome' So I bought it $6.99.
Do you have a story about the best yet obscure record from your collection ?