[This is a comprehensive list of artists whom I personally consider to be "psychedelic". Judge for yourself, though, because such things are highly subjective.]
DEFINITELY Psychedelic artists:
John Alcom
S. Allen
Arab [re. Blue Cheer's Outside Inside artwork]
Richard Avedon
Peter Bailey
Carol Behan [also see "Fish Prods."]
Steve Benton [re. holography; creator of Benton-type holograms]
Peter Blake [designed both the 3-D/holographic LP cover of The Rolling Stones' Their Satanic Majesty's Request and the album cover of The Beatles' Sgt. Pepper's Lonely Hearts Club Band]
Jim Bl[a?]shfield [created the artwork of several Fillmore posters]
Michael Bowen
Phil [Brown?] [re. my purple tie-dyed psychedelic t-shirt]
Bunnell
David Byrd
CCCP [re. Kantner & Grace's Sunfighter artwork]
Michael Chechik [Fillmore KPFA Benefit 10/30/67 artwork]
Piermario Ciani [re. The Psychedelic Years artwork]
Allen Cohen
Nancy Coner
Lee Conklin
Bruce Connor [created artwork for the Trips Festival program]
Robert "R. Crumb" Crumb [re. comic art]
Anonim Cuba
J. Cushing
Salvador Dali
Heinz Edelman [common alternate spelling of "Heinz Edelmann"]
the Fool [Dutch foursome which: painted the outside of the Beatles' "'Apple' boutique", painted John Lennon's psychedelic Rolls-Royce, designed the cover of the album The 5000 Spirits or the Layers of the Onion by The Incredible String Band, & recorded their own musical album]
Robert "Bob" Fried
GDM Inc. [probably "Grateful Dead Merchandising Inc."]
Theodor Geisel [real name of "Dr. Seuss" & "Theodor Lesieg"]
Jeremiah J. Gill [contemporary American artist (mostly paintings) consistently psychedelic; Springfield, Missouri, USA]
Loren Gillette
Milton Glaser(/Glazer) [USA]
Jon Goodchild
Bonnie MacLean Graham [synonym of "Bonnie MacLean"]
Alex Gray/Grey
Mick Gray, Alan Moore, & J.H. Williams III [re. Promethea comic book issue #16]
Herb Greene [important, probably the most important, US 60s-rock photographer]
Rick Griffin [USA]
Gary Grimshaw
Also Gutt/ Also-Gut
Jon Hanna [mentioned by Reid Stuart]
Robin Constable Hanson [re. kaleidoscope art, esp. video]
Hapshash and the Coloured Coat [Michael English & Nigel Waymouth]
Jack Hatfield
Maximillian Hellweger
Leon Hendrix E-S-C
Hirokatsu Hijikata [Japan]
Hipgnosis [re. Pink Floyd's artwork]
J. Flournoy Holmes [also see "D. Powell" and "Wondergraphics"]
Grass Hopper
Hovel
George Hunter
Robert Indiana
Greg Irons
Jack "Jaxon" Jackson [synonymous with "Jaxon"]
"Jaxon": see "Jack Jackson"
Dana W. Johnson
Paul Kagan
Gunther Keiser [re. AOR 3.185: Hendrix poster w/ wires]
Alton "Kelly" Kelley [real name of "Kelly"; American psychedelic artist; USA]
"Kelly": see "Alton Kelley"
Ryan Kerrigan [re. psychedelic artwork; has done artwork for the Home Grown News Network]
Jaxon B. Kliban
T.W. Korpalski
Nicholas Kouninos [artwork on both BG 92-1 & BG 94-1]
Cindy LaBreacht [created the artwork on the cover of Trips... by Cheryl Pellerin]
Jean Larcher [re. Op Art]
Lawrence
Dr. Timothy Leary
Jan Lenica
Eli Leon
Theodor Lesieg [pseudonym of Theodor "Dr. Seuss" Geisel used for works he illustrated but didn't write]
Carl Lundgren
Bonnie Graham MacLean [USA; the current name of "Bonnie MacLean Graham"]
Marjorie [re. "California Hall"]
Joey Mars [re. contemporary psychedelic artwork]
Bob Masse
MATI [re. cover artwork on Santana's Abraxas album]
Peter Max [American psychedelic artist; USA]
McCartney, Sir Paul [designed the wrapping paper for the Indica bookstore; member of The Beatles]
J.W. McHugh
Mike McInnerney
Joyce Miller
Sandy Miller
Stanley "Mouse" Miller [real name of both "Mouse" and with "Stanley Mouse"; American psychedelic artist; USA] [also see "Mouse Studios"]
Barbara Mitchell [re. kaleidoscope art, esp. video]
Ufo Mka II
Moire' [re. Op Art]
Victor Moscoso
Levon Mosgofian
"Mouse": see "Stanley Miller"
Stanley Mouse: see "Stanley Miller"
Myers & Johansen III
Jimms Nelson [Fillmore East artwork]
Nick Nickolds
Denis Nolan [an alternate spelling of "Dennis Nolan"]
Dennis Nolan [an alternate spelling of "Denis Nolan"]
Dan O'Neill [re. Jefferson Airplane's Volunteers cartoon]
Norman Orr
Osiris Visions [publisher re. UFO club]
Palladini
Adam Peiperl [re. kaleidoscope art, esp. video]
Edawrd Phelps, Jr.
Pierre
Betsy Pike
Wilfred "Satty" Podreich [the real name of both "Satty" & "Wilfred Satty"]
Lawrence "Larry" Poons [re. Optical Art]
D. Powell [also see "J. Flournoy Holmes" and "Wondergraphics"]
Terry Quirk
Raven
L.S. Rehbock
Ted Richards
Bridget Riley [re. Optical Art]
Willyum Rowe
Ed Sanders
"Satty": pseudonym of "Wilfred Podreich"
Wilfred Satty: pseudonym of "Wilfred Podreich"
Howard Schatz [re. Optical Art]
Bob Schnepf [synonymous with, and probably the real spelling of, "Bob Schnepft"]
Bob Schnepft [rare synonym, probably misspelling, of "Bob Schnepf"]
Seymour Schwast [USA]
Clifford Charles Seeley
Josep Segrelles [Barcelona, Spain]
"Dr. Seuss": pseudonym of "Theodor Geisel" used for works he both wrote and illustrated
Martin Sharp
Gilbert Shelton
David Singer
R.K. Sloane
David Smith
Elmer W. Smith [re. botanical illustrations of hallucinogenic species & subspecies]
Jon Stahl
Felix Stover [Germany]
Mari Tepper
Bradbury Thompson
John Thompson
Randy Tuten
Van Ben [re. 3rd Dimension Graphics' psychedelic Jesus poster]
John Van Hamersveld
Victor Vasarely [re. Optical Art; synonymous with, and probably the correct spelling of, "Victor Vassarely"]
Victor Vassarely [common synonym, and probably misspelling, of "Victor Vasarely"]
Robert Venosa [mentioned by Reid Stuart]
"Volk"? [sp?] [mentioned by Reid Stuart]
Louis Wain [20th-century mentally-ill artist; psychedelic artwork of cats]
Bill Walker [re. The Grateful Dead's Anthem of the Sun artwork]
Nigel Waymouth [probably synonymous with "Nigel Weymouth"]
Wess Weiser
Tom Weller [also see "Joyful Wisdom Ent."]
The West Will Sun Graffix [recommended by Wes Wilson]
Nigel Weymouth [probably synonymous with "Nigel Waymouth"]
Harvey S. Williams
Jason Brian Wilson [son of Wes Wilson; artist; Springfield, Missouri, USA]
Wes Wilson [Aurora, Missouri, USA]
Yando
Zacron/ZACRON [re. Led Zeppelin's Led Zeppelin III artwork]
PROBABLY Psychedelic artists:
Josef Albers [re. Optical Art]
Richard Anuszkiewicz [re. Optical Art]
Aubrey Beardsley
Daniel Clyne
Max Conlon [re. Australian aboriginal art]
Pam Hall [re. Australian aboriginal art]
Francois Morellet [re. Optical Art]
Kenneth Noland [re. Optical Art]
"Savage Pencil"
Manuel "Spain" Rodriguez [re. comic art]
Jesus-Rafael Soto [re. Optical Art]
Andy Warhol
Robert Williams [re. comic art]
S. Clay Wilson [re. comic art]
SOMEWHAT Psychedelic artists:
E. Barque [Vilafranca of the Penedes]
A.M. Cassandre: see "Adolphe Jean-Marie Mouron"
Seymour Chwast
H.R. Giger
E. McKnight Kauffer [USA]
Adolphe Jean-Marie Mouron, a.k.a. A.M. Cassandre
Chris Pederson
Gary B. Trudeau [re. Doonesbury comic art]
POSSIBLY Psychedelic artists:
Joan Chase
George Conger [re. The Grateful Dead's American Beauty photograph]
Gustav Klimt
Mary Anne Mayer
Alphonse Mucha
John Toorop
Misc. Psychedelic TERMS:
PSYCHEDELIC PRODUCTION COMPANIES, SHOWS, & PERIODICAL-COLUMNS:
Berkeley Bonaparte company/ Berkely-Bonaparte
Bill Graham Presents [also see "The Fillmore", "The Fillmore East", "The Fillmore West", & "The Winterland"]
C&D Visionary
Family Dog Productions [also see "The Avalon Ballroom"]
Fantasy Unlimited
Fish Prods. [also see "Carol Behan"]
the Fool [Dutch foursome which: painted the outside of the Beatles' "'Apple' boutique", painted John Lennon's psychedelic Rolls-Royce, designed the cover of the album The 5000 Spirits or the Layers of the Onion by The Incredible String Band, & recorded their own musical album]
GDM Inc. [probably "Grateful Dead Merchandising Inc."]
"Graham, Bill": see "Bill Graham Presents" under "B"
Hapshash and the Coloured Coat [Michael English & Nigel Waymouth]
High Art [re. High Times magazine]
Hipgnosis [re. Pink Floyd's artwork]
The Joint Show [Griffin, Kelly, Moscoso, Mouse, & Wilson]
The Joint Show II [Griffin, Kelly, Moscoso, Mouse, & Wilson]
Joyful Wisdom Ent. [also see "Tom Weller"]
Mouse Studios
Neon Rose [also see "The Matrix"]
Osiris Visions [publisher re. UFO club]
Wondergraphics [also see "J. Flournoy Holmes" and "D. Powell"]
and others
PSYCHEDELIC GALLERIES & PUBLICATIONS:
Cosmic Paper
The Fitz Hugh Ludlow Memorial Library
The Moore Gallery
The Museum of Rock Art (Daytona Beach, Florida)
Off The Wall [defunct poster-art-related periodical published by Wes Wilson out of Aurora, Missouri]
The Postermat Gallery/ The Postermat
The Print Mint
The Psychedelic Shop
Psychedelic Solution/Solutions
The San Francisco Art Institute
The San Francisco Oracle
and many others
TYPES OF PSYCHEDELIC DESIGNS, GENRES, Etc.:
abstract art
acid rock
arabesques
Art Psychedelic
Benton holograms [one type of holograms; named after creator Steve Benton]