Psychedelic rock is a genre often inspired or influenced by psychotropic narcotics, particularly LSD and/or Marijuana.
The musical style often incorporates flowing, hypnotic rhythms and use of guitar, vocal and organ effects, most notably the Wah-Wah pedal which is either used to make a fast, funky but psychedelic sound or used slowly to create a psychedelic wave of guitar sound, and Hammond organ used to make Blues psychedelic harmony.
Some notable psychedelic rock bands would include - 13th Floor Elevators or The Charlatans (not the more recent UK band with the same name), These 2 bands produced psychedelic rock albums around 1964/1965, this was 2 years before The Beatles released Revolver which included a very psychedelic song called Tomorrow Never Knows. Other notable acts would include The Jimi Hendrix Experience, some of the work by Cream and of course Pink Floyd, there is of course Hawkwind, who sometimes get referred to as "Space Rock", and let's not forget Janis Joplin.
The Beach Boys
Captain Beefheart & His Magic Band
The Crazy World of Arthur Brown
The Incredible String Band
The Jimi Hendrix Experience
The Mamas & The Papas
The Moody Blues
The Mothers of Invention
The Pretty Things