Pink Floyd and David Byrne (well, the Talking Heads) already got a mention… but if anybody is into “drug” music, they need to check out Yello.
All time best hands down, IMHO, the Butthole Surfers.
Honorable Mention:
Skinny Puppy
The Jesus Lizard
Scratch Acid
13th Floor Elevators
Monster Magnet
The MC5
Velvet Underground
Pink Floyd
The Flaming Lips
Einstürzende Neubauten
Frank Zappa
Frank Zappa and the Mothers
Laibach
Black Sabbath
Misistry
The Revolting Cocks
The Loco Gringos
old Blue Oyster Cult
Peter Gabriel, pre-So.
old Genesis (Selling England by the Pound, Trick of the Tail, Lamb lies Down on Broadway)
Killing Joke
the Stranglers
Bauhaus
some more votes for:
Grateful Dead
Zappa
Hendrix
Add me to the Moody Blues list.
Abso-fucking-lutely. Especially White Light / White Heat and especially especially the song I Heard Her Call My Name… on acid, anyway.
Also
Dukes of the Stratosphear (XTC)
The 13th Floor Elevators
The Stranglers
Calexico
The Residents
Camper Van Beethoven
Black Grape
The Legendary Pink Dots
The Stooges
The Nuggets Compilations
and pretty much anything Nitroglycerine recommended… as usual (thanks for mentioning Flipper).
Many of my favs have been mentioned already (The Doors, The Floyd, The Talking Heads, Bob Marley) but I gots a few more.
U2 - Unforgettable Fire. I still get the feeling of being stoned when I listen to this album.
Beatles - The music that they made when they were on drugs is fantastic.
Alice in Chains - I don’t know what to say except they had it all, and to me Laynes fondness for the smack permeates into just about all of their songs.
Dandy Warhols - Especially ‘Fast Driving Rave Up’, the song just makes me want to move even if I can’t 
Actually, have you tried listening to the “Alien 4” and “Love in Space” albums? They actually managed to get good again briefly before descending into wankitude once more.
If you want recent versions of the good stuff, I highly recommend Nik Turner’s “Space Ritual 2001” and “Past or Future” albums. (Well, it’s been long enough that they’re not exactly “recent” any more, but they’re more recent than the original “Space Ritual”.)
I snuck them out when you were nodding …
Shpongle
Or Infected Mushroom
A Chicago DJ who calls himself Nightmares on Wax did an album called “Smokers Delight.” It’s in my top three triphop/drumnbass/djgroove of ALL TIME. It’s an entire classic.
I forgot about DJ Shadow. That’ll do it.
Damn, I can’t believe I forgot about Killing Joke. Especially the Fire Dances album.
If I still did acid, I’d like to trip and listen to this Andy Prieboy (Wall Of Voodoo’s second singer) album I got a few weeks ago.
Aphex Twin’s Selected Ambient Works, Vol. 2
Oh, and Peter Gabriel’s Passion.
Tiesto is great. Also Armin van Buuren.
When I was in college (long ago), It’s A Beautiful Day (name of both band and album) was very popular. I now own the CD, and I’ve noticed that if I play it around the younger generation, they look at me kinda funny. I can’t think of another album that quite so clearly conveys the message: “I was smokin’ dope.”
Pot:
Radiohead
The Police
Beastie Boys
Postal Service
The Notwist - Neon Golden
Dave Matthews
The Strokes
Chemical Brothers
Trippy hip-hop/rap
Nitrous:
Any good techno or hip-hop with a bumpin’ bass line!
Cocaine:
Anything that really rocks out. There’s some very good Japanese rock for this. Godsmack is also good. Haven’t done enough cocaine to comment in much more depth (don’t plan to, really).
Methamphetamine: (It was a one-time thing, really!)
Hardcore rock-out music at high volume in the “coming up” period. Plenty of good rock and rap for this.
“Chill-out” rock for the comedown (and anything that’s good for pot, because one should be smoking plenty of pot on a meth comedown anyway).
Radiohead - Hail to the Thief
Ketamine:
Trippy music or music that’s good on nitrous, works here. Vitamin K isn’t a very musical drug, though, and whatever music you pick doesn’t really contribute to the experience that much.
DXM:
Yeah Yeah Yeahs
Chemical Brothers
“Chill-out” rock or trippy stuff (or, even better, trippy chill-out rock).
Boy, my brother’s had me listening to half these bands all my life…and he doesn’t smoke, he’s just a big nerd. I wonder what our parents thought about us being 13/15 and hanging out in his room listening to this stuff (10 years ago, not in the 70s…)
Sublime is my vote for getting me “in the mood” except sometimes they just rock out and that’s not so good for when you’re trying to mellow. But those guys liked to tweak too…
Thought of another one: Banco de Gaia