For shame... no one's mentioned Charlie Parker yet? Tsk, tsk...
Here's a starting guide for jazz, divided into sub-genres (also, for a first listen, I'd go with what people are telling you and listen to Kind of Blue, but you've already checked that out by now, haven't you?
Traditional/Dixieland:
Louis Armstrong
Bix Beiderbecke
Jelly Roll Morton
Sidney Bechet
Big Band/Swing:
Duke Ellington
Count Basie
Benny Goodman (overrated, but personifies the genre pretty well)
Vocal Jazz:
Ella Fitzgerald
Billie Holiday
Sarah Vaughan
Bebop:
Charlie Parker
Dizzy Gillespie
Thelonious Monk
Hard Bop:
Art Blakey
50's Charles Mingus stuff (Mingus Ah Um, in particular)
Cannonball Adderley
Free Jazz:
Ornette Coleman
Coltrane's later stuff
Sun Ra
Cecil Taylor
Fusion:
Miles Davis (Davis has excellent work that fits into most jazz genres from 1945 on until his death, so he also applies to Bebop and Hard Bop, Cool Jazz, and Post-Bop)
The Mahavishnu Orchestra
Return to Forever
Weather Report
That's just the tip of the iceberg, there are a ton more sub-genres and great artists that I didn't mention. But pick out any of those, and you'll be hearing some fine, fine music. There are artists such as Miles Davis and John Coltrane that have covered several different genres, so I didn't categorize them in any place particular (except for Miles in fusion, because he created it and was the best at it, IMO). Enjoy, I believe you've got some downloading/buying to do.
P.S. Parliament and Funkadelic aren't jazz, but I could dig on the funk for weeks straight.