I'm a roots guy (blues, old school R&B and country, rock, etc.) and the jazz thing never spoke to me, so I don't have the horn players in my list (I guess Miles would make the list, because his sound was just beautiful).
If I look strictly at musicianship, I'd say:
Jeff Beck (Blow By Blow, numerous live performances over the years)
Ray Charles (America, the Beautiful, In The Heat of the Night)
James Jamerson (What's Goin' On, Ain't No Woman Like the One I've Got)
Dr. John (Walk On Gilded Splinters, Accentuate the Positive, live performances)
Stewart Copeland (Murder By Numbers, Every Little Thing She Does Is Magic)
Freddie Mercury (Somebody To Love, Crazy Little Thing Called Love)
As for musicians/songwriters:
Kurt Neumann (The BoDeans): wonderful clean guitar sound, great songs, Idaho, Dreams)
Lindsay Buckingham: One of the most unique guitarists in rock (Go Insane, Go Your Own Way)
Mark Sandman (His songs just reach me: I Think She Likes Me, You Look Like Rain)
Tom Petty/Mike Campbell (This pair might be my favorite rock combination of songwriting and sound: Refugee, Here Comes My Girl)
Tom Waits (Heart of Saturday Night, Way Down in the Hole)
Sarah McLachlan (just beauty in sound, Building a Mystery, Ice Cream)