There's an excellent obituary for Joe Zawinul in The Independent. It maps out the broad range of music he was involved with throughout his life. He may have been in Weather Report, played with Dinah Washington and wrote "Mercy, Mercy, Mercy" for "Cannonball" Adderley however, nothing compares to his composition and playing on, "In a Silent Way" which was recorded in 1969 by Miles Davis. If you've never heard "Silent Way" you've been missing out on a stunningly beautiful composition/album. The album is made up of two album-side long compositions and is like no other music that Miles Davis made. In fact, the closest thing I can think of was Joe Zawinul's first solo album that came out a year later simply titles Zawinul.
I just checked Amazon and Zawinul is still available. It continues the concepts first put in place with Miles Davis and according to some sources, was what set the groundwork for the jazz "supergroup", Weather Report, which featured Zawinul and Wayne Shorter.