I've listened to loads of psychedelic music from electronic to the original stuff. however the one song that stands out to me is 1983 by hendrix. I recently listened to it during an acid trip (acid's the best for music as I'm sure those who've experienced it!). It was the craziest thing I've ever heard:
[YOUTUBE]
it slows down so much while tripping and you just get lost in the "down and down we go" forever and ever. amazing song. hendrix was one of the best musicians ever and he loved acid, put those together and you got this.