As a general rule, if you're into crazily psychedelic instrumental kind of stuff, you want to look for the lesser known bands.
Putting that aside, though, I recommend Piper at the Gates of Dawn by Pink Floyd or The Madcap Laughs by Syd Barrett. More pop-ish psychedelic can include Anthem of the Sun by Grateful Dead, Cream's Wheels of Fire and Disraeli Gears, Strange Days by the Doors, etc. Also, I don't like to think of the latter Floyd albums as "trippy", if you get what I'm saying.