The music you had to put on when you were buzzing. The music that expanded your mind.
My choice?
Traffic.
mozart
You know…were I still toking…I’d try him.
Jefferson Airplane.
Cab Calloway.
But only with cocaine or opium.
Butthole Surfers. 
Pink Floyd
Grateful Dead
Radiohead
It all depends on what kind of drug you’re talking about of course, but those were the three on constant rotation back in my less respectable days.
I used to have the album “This is the Moody Blues”. It was good for the deep introspection that went with my dope smoking.
Pink Floyd
Generic “jam band” music (Phish, The Dead, Rusted Root, Blues Traveler etc)
Dr Dre / Snoop Dogg
Smashing Pumpkins
Beastie Boys
Sonic Youth
(Ms. cornflakes votes for Philip Glass or Jethro Tull.)
Pink Floyd. Esp. Shine on You Crazy Diamond & the entire Dark Side of the Moon CD.
Roxy Music is also quite good.
Dire Straits’ Brothers In Arms
Steely Dan. Anything, really.
Pink Floyd, Bob Marley, Phish, and Nirvana
With psychedlics:
Pink Floyd
Shpongle
good trance
As a complete coincidence, I’m listening to Dark Side of the Moon and drinking a beer as I write this. Yeah, it’s only one beer, but I did give blood earlier this afternoon, so it won’t take me much to ‘feel the flow’ so to speak.
Mike Oldfield: Tubular Bells (I & II)
A University roommate had both of those, we wasted a lot of time with them (in a manner of speaking).
Black Sabbath*
Deep Purple
Ritchie Blackmore’s Rainbow**
Pink Floyd
Donovan
War
Beethoven
*When Ozzy was with the band. Accept no short, curly-haired, balding, leather-lunged substitues who should have stayed with Ritchie Blackmore’s Rainbow.
**not to be confused with Rainbow, which was the travesty that happened after Ronnie James Dio split the band.
My top 20, 1984-1987:
Bob Marley
Led Zeppelin
Pink Floyd
Jimi Hendrix
The Who(67-73 recordings)
Cream
Talking Heads
The Doors
Santana (67-72 recordings)
Peter Gabriel
Jethro Tull(Thick as a Brick)
The Police
Mozart (Symphonies 35-41)
Jean Michel Jarre (Oxygene)
Omm Kalthoum (Inta Omry)
King Sunny Ade
The Allman Brothers
The Eurythmics
Traffic
Spirit
Barry Manilow.
Yes, I’m kidding. 
Second on the Moody Blues and pot.