1E DMG lists these books for general DnD
Anderson, Poul. THREE HEARTS AND THREE LIONS; THE HIGHCRUSADE; THE BROKEN SWORD
Bellairs, John. THE FACE IN THE FROST
Brackett, Leigh.
Brown, Fredric.
Burroughs, Edgar Rice. "Pellucidar" Series; Mars Series; Venus Series
Carter, Lin. "World's End'' Series
de Camp, L. Sprague. LEST DARKNESS FALL; FALLIBLE FIEND; etal.
de Camp & Pratt. "Harold Shea" Series; CARNELIAN CUBE
Derleth, August.
Dunsany, Lord.
Farmer, P. J. "The World of the Tiers" Series; etal.
Fox, Gardner. "Kothar" Series; "Kyrik" Series; et of.
Howard, R. E. "Conan" Series
Lanier, Sterling. HIEROS JOURNEY
Leiber, Fritz. "Fafhrd &Gray Mouser" Series; et of.
Lovecraft, H. P.
Merritt, A. CREEP, SHADOW, CREEP; MOON POOL; DWELLERS IN THE MIRAGE
Moorcock, Michael. STORMBRINGER; STEALER OF SOULS; "Hawkmoon"
Norton, Andre.
Offutt, Andrew J., editor SWORDS AGAINST DARKNESS Ill.
Pratt, Fletcher, BLUE STAR; etaf.
Saberhagen, Fred. CHANGELING EARTH; etal.
St. Clair, Margaret. THE SHADOW PEOPLE; SIGN OF THE LABRYS
Tolkien, J. R. R. THE HOBBIT; "Ring Trilogy"
Vance, Jack. THE EYES OF THE OVERWORLD; THE DYING EARTH
Weinbaum, Stanley.
Wellman, Manly Wade.
Williamson, Jack.
Zelazny, Roger. JACK OF SHADOWS; "Amber" Series
except Amber which ones are for the planes, or do you know any more novels written since then
Michael Moorcock's Eternal Champion cycle is the primary inspiration for D&D's multiverse. It's all about the same endlessly reincarnating main character, who often travels from plane to plane fighting for Balance in the eternal war between Law and Chaos, but Moorcock's most beloved series is Elric of Melniboné .
Cataloging Moorcock's books is difficult because they've been released under a variety of different titles and as part of differently-tilted omnibus collections, but here are some key Moorcock novels from a planar perspective:
Erekosë: The Eternal Champion, The Dragon in the Sword
Elric: Elric of Melniboné, The Sailor on the Seas of Fate, The Weird of the White Wolf, The Vanishing Tower, The Bane of the Black Sword, Stormbringer, The Fotress of the Pearl, The Revenge of the Rose
Corum: The Knight of Swords, The Queen of Swords, the King of Swords, The Bull and the Spear, the Oak and the Ram, The Sword and the Stallion
The Dancers at the End of Time
The Second Ether: Blood: A Southern Fantasy
Of these, I thought The Dragon in the Sword and The Revenge of the Rose were particularly Planescapey. Blood: A Southern Fantasy is incredibly weird, but kind of a conceptual breakthrough when it comes to depicting planar travel.
Philip Jose Farmer's "World of Tiers" is relevant from a planar perspective, though I've read some bad reviews of it.
H.P. Lovecraft should be read, of course, particularly "The Dream-Quest of Unknown Kadath," "The Music of Erich Zann," and "The Silver Key."
Jack Vance's The Dying Earth: The Dying Earth, Eyes of the Overworld, Cugel's Saga, Rhialto the Marvelous.
Poul Anderson: The Broken Sword, Three Hearts and Three Lions, War of the Gods
L. Sprague deCamp and Fletcher Pratt: The Complete Compleat Enchanter ("The Roaring Trumpet," "The Mathematics of Magic," "The Castle of Iron," "The Wall of Serpents," "The Green Magician.") The hero of these stories, Harold Shea, travels to various mythological realms, exploring Norse, Finnish, and Irish mythology, as well as Coleridge's poem "Kublai Khan" and the Orlando cycle.
John DeChancie: Castle Perilous, Castle For Rent, Castle Kidnapped, Castle War
Robert Asprin: Another Fine Myth, etc (MythAdventures series).
Neil Gaiman: The Sandman (comics), Books of Magic (comics), Neverwhere, A Walking Tour of the Shambles (with Gene Wolfe), Stardust, Anansi Boys, Good Omens (with Terry Pratchett)
John Ney Rieber and Peter Gross: The Books of Magic (comics)
Mike Carey: Lucifer (comics)
Mike Mignola: Hellboy (comics)
Terry Pratchett: The Colour of Magic, The Light Fantastic, Mort, Reaper Man, Small Gods, Hogfather, Eric, Lords and Ladies, Thief of Time
Alan Moore: Promethea (comics)
China Mieville: Perdido Street Station
Gene Wolfe: The Book of the New Sun
Simon R. Green: Something From the Nightside, Agents of Light and Darkness, Nightingale's Lament, etc. (the Nightside series).
Hal Duncan: Vellum, Ink, Escape from Hell!
Jeff VanderMeer: City of Saints & Madmen; Shriek: An Afterword; Finch
M. John Harrison: Viriconium
Italo Calvino: Invisible Cities
Milorad Pavic: Dictionary of the Khazars
Jorge Luis Borges: Short Stories
Lawrence Miles: The Book of the War
Franz Kafka: Complete Stories
Clive Barker: The Hellbound Heart, Weaveworld, The Great and Secret Show, Everville, Imajica
Michael Cisco: The San Veneficio Canon, The Tyrant
Movies
City of Lost Children, Dark City, Spirited Away, What Dreams May Come, Pan's Labyrinth