Now this would depend on what I'm high on (hahaha)-
Drunk- Pantera - as well as anything else with the "lets get really drunk and attack things with sledge hammers" ethos
Stoned- Probably Kyuss, as well as other stoner (obvious really), although I agree with the idea of anything with lots of layers- you don't really hear EVERYTHING til your stoned, so almost any band can take on a new dimension.
Uppers- Slayer- although i just love them anyway, anything above 180bpm will do the trick, so thrash or death in terms of metal (although the latter can be harder to find a headbanging beat in), otherwise you've got to go to dance music
Hallucinogens- tricky, depends on how energetic you feel, and nothing that will freak you out with lots of different sounds, or that requires ANY concentration. Really an individual thing