I will have a very hard time narrowing it down to just 10, since I listen to 3 main genres of music, and each one has bands, musicians, composers that I have probably listened to at nearly equal rates.
So, I am going to "cheat" (one list per genre):
Prog:
Yes
King Crimson
PFM
Magma
Banco
Gentle Giant
Genesis
Frank Zappa
Univers Zero
Pain of Salvation
Jazz:
John Coltrane
Allan Holdsworth
Mahavishnu Orchestra
Return to Forever
Steve Coleman
Anthony Braxton
McCoy Tyner
Keith Jarrett
Oregon
Jean Luc Ponty
Classical:
Elliott Carter
Joan Tower
Bruno Maderna
Charles Wuorinen
Arnold Schoenberg
Gyorgi Ligeti
Krzysztof Penderecki
Bela Bartok
Igor Stravinsky
Kaija Saariaho