BEST little know Jazz Album that you ever heard?

Another that might be considered “little known” as a jazz album, but certainly not unfamiliar in terms of the music it contains is “A Charlie Brown Christmas” by the Vince Guaraldi Trio. 
 

‘Tis the Season!

I second Blue Mitchell with The Thing To Do (RGV Edition)

Not much of a jazz-hound but John McLaughlin's first album: Extrapolation. 

Charlie Haden "The Montreal Tapes with Don Cherry and Ed Blackwell" (one of several "Montreal Tapes" recordings).  It's essentially the Ornette Coleman quartet without, well..........Ornette Coleman!  They pull it off on a well-recorded piece that's worth exploring.

Frank Morgan "Mood Indigo".  Way, way WAY underrated and relatively little-known alto sax player who was something of a Charlie Parker protege'.

Woody Shaw "In My Own Sweet Way".  Another (underrated) trumpet player who was held in very high regard by none other than Miles Davis.

@tylermunns 

Thanks for the heads up. I will check the show out.

Only some of my list I would consider avant-garde. Maybe "progressive" would be the best description for most of my list.

I got to say, though, I am constantly surprised on how few jazz fans that post on music forums, are into exploring new stuff. So many great, creative subgenres. So many musicians with chops as good as the masters from the past.