Without live music, this was actually pretty easy. But then, with live music, it probably would've all been Grateful Dead, Shakti, Allman Brothers and Keith Jarrett.
1 Mars Volta - Cassandra Geminni
2 Yes - Close to the Edge
3 Godspeed You! Black Emperor - Rockets Fall on Rocket Falls
4 Herbie Hancock - Wandering Spirit Song
5 Nusrat Fateh Ali Khan - Jewleh Lal
6 Miles Davis - In A Silent Way
7 King Crimson - Lizard
8 Godspeed You! Black Emperor - Storm
9 Miles Davis – Bitches Brew
A group over 15 minutes that doesn't make the cutoff, but would have all been contenders.
Miles Davis - Shhh/Peaceful
Charles Mingus – Modes D, E and F of Black Saint and the Sinner Lady (I was tempted to include the entire album, as it's all one suite, but whatever)
Sergei Rachmaninoff – Piano Concerto No. 3, 1st Movement
Miles Davis – Spanish Key
LTE – When the Water Breaks