Several people have mentioned the "United States of America" album, but I also love the
followup "American Metaphysical Circus", credited to Joe Byrd & The Field Hippies (Byrd was synth
player, singer & composer for USA)...
13th Floor Elevators
White Noise
Kaleidoscope (both bands, American and British)
Nirvana
Bubble Puppy (Texas Psych with top 25 hit "Hot Smoke and Sassafras")
Gandalf
early Deep Purple
...and don't forget Spirit (although calling them Psych is almost an insult; they're that & more!!)
Fever Tree (criminally underrated; first album is classic, second is also good)
I got the Nuggets on 3 separate CD's years ago, then they released that box with extra stuff.
Some folks don't like comp's, but there are so many psych bands that had just one hit or one
good song, like Balloon Farm ("A Question of Temperature").