This is probably the best site I've ever found. tela.sugarmegs.org/boxofrain/ It's got to be one of the largest Phish/Grateful Dead archives online, though it's only open for downloading stuff on weekdays from 5PM-9AM and all weekend. It's got a TON of music to download. From just last year's bonnaroo I found:
Andrew Bird Beck Bela Fleck Ben Folds Blues Traveler Super Jam Bright Eyes Cat Power Devendra Banhart The Disco Biscuits Elvis Costello G Love and Special Sauce Grace Potter and the Nocturnals The List goes on!!!
I got tired of looking through it all, so I stopped at the half way point. You guys have got to check this site out! It will blow your mind, SO MUCH FREE MUSIC! and totally LEGAL!
Alison Krause & Union Station 4-7-90 David Grisman & Stephan Grapelli 8-19-77 Elton John 11-12-70 (pre-superstar! :D) Planet Earth Rock-n-Roll Orchestra ---listed as perro...it's Jerry Garcia, Phil Lesh, David Crosby, Grace Slick, Jorma Kaukonen, more.....
edit - ...and even though the download times are restricted, everything is always available for streaming
*i like coconuts, you can break them open they smell like ladies lyin in the sun** *Hell I don't even know where I am** *for now I must sit here and ponder the yonder: The herbivores did well cause their food didn't never run** *We listen, if it feels good We shake** *You made a big impression for a girl of your size, Now I can't get by without you and your big brown eyes.**