Illssender (Hellbound: The Dark of the War, page 24) A balor, one of the greatest warleaders of his kind, ruler of a tower on the 313th layer of the Abyss (if not the entire layer).
Taramanda (Hellbound: The Dark of the War, page 24) A marilith general, ruler of a sprawling fortress in Blood Tor, catalogued as the 13th layer of the Abyss.
The Marquesse of Loss (ibid.) One of the subtlest and most influential of the nalfeshnee lords of Woeful Escarond, catalogued as the 400th layer of the Abyss.
Oulstra (ibid.) A balor, once a nalfeshnee rival of the Marquesse of Loss. Continues to have a bitter rivalry with her former colleague.
Judge Gabberslug (Uncaged: Faces of Sigil) A former nalfeshnee Lord of Woe (like the Marquesse of Loss and Oulstra), exiled to Sigil and the Negative Energy Plane.
Alusiel (Faces of Evil: the Fiends, page 63) A fallen trumpet archon, ruler of the city Mal Arundak in the Rainless Waste (catalogued as the 403rd layer). Alusiel is growing increasingly demonic with the passing years.
Thralhavoc (Hellbound: War Games, page 56) Former ruler of the 348th layer of the Abyss, abandoned it deliberately to focus on his more important layers.
Taphaeon (Hellbound [ibid], the Manual of the Planes, Book of Vile Darkness) A nalfeshnee, wielder of the Despoiler of Flesh, ruler of the Fortress of Indifference.
Tarnhem: The balor who formally ruled the layer called Noisome Vale, which is mentioned in the Manual of the Planes and originally appeared in the
Dungeon Master's Guidebook by Bruce Cordell.
The Knight Errant: A humanoid demon bound about with rings of cold fire and dripping with lightning. It allows no one who look at it to live, no matter how far it must hunt those who try to flee. From Faces of Evil: The Fiends.
Jaranda (Planes of Chaos, the Book of Chaos, page 24) The marilith ruler of the fortress of Gallowsgate on the Plain of Infinite Portals, she is friendly to the Doomguard.
Red Shroud (Planes of Chaos, the Book of Chaos, page 25 - also the Manual of the Planes) The succubus ruler of the fortress-city of Broken Reach, a sorcerer.
Maretta (Planes of Chaos, The Book of Chaos, page 28) The succubus Lady of the Counting-House in Graz'zt's realm.
Rotting Jack (Ibid, page 29) A babau, formally a servant of Orcus, then a servant of Kiaransalee. Present status unknown.
The Amber Stallion (Ibid, page 32) An armanite, ruler of the largest and successful herd in the layer of Gallenshu.
Vis Nirrin Vis (Ibid) The greatest warleader of the varrangoin.
Keekaku (Ibid, page 33) The nabassu Nursemother, a powerful, enormous, bloated demon dwelling in Pazuzu's realm of Torremor.
Eltab (Champions of Ruin, page 130) Lord of the Hidden Layer.
Ahrimanes: Note that she is called the "Demon Lady Ahrimanes" in Gary Holian's articles for Dragon Magazine, including the Death Knights one.
The Kerzit is not a demon lord, only a powerful unique demon.
Orcus and Demogorgon also appeared in the basic D&D rules (I forget exactly where)
They're in the Immortal's boxed set as Immortals of Entropy. Demogorgon, there, is technically Orcus' superior, and is female.
Here are all the official or semi-official Abyssal layers I could pick out of my huge list of non-official layers. If not otherwise noted, they come from
Planes of Chaos.
LAYER 1: PLAIN OF INFINITE PORTALS
LAYER 2: DRILLER'S HIVES
LAYER 3: FORGOTTEN LAND
LAYER 4: GRAND ABYSS
LAYER 5: WORMBLOOD
LAYER 6: REALM OF A MILLION EYES (THE GREAT MOTHER'S REALM)
LAYER 7: PHANTOM PLANE (KEARACKININ; SESS'INEK'S REALM)
LAYER 8: "SKIN-SHEDDER" (I)
LAYER 9: BURNINGWATER (I)
LAYER 10: "THAT HELLHOLE" (I)
LAYER 11: MOLRAT (I)
LAYER 12: TWELVETREES
LAYER 13: BLOOD TOR (Beshaba and Umberlee's realms; F&A)
LAYER 23: IRON WASTES (Kostchtchie's realm)
LAYER 27: MALIGNEBULA (Lissa'aere the Noxious' realm; Hellbound)
LAYERS 45, 46 AND 47: AZZAGRAT (TRIPLE REALM) (Graz'zt's realm; For Duty and Deity)
LAYER 57: TORTUROUS TRUTH (Duke Alvarez's realm; FoE)
LAYER 65: LOLTH'S WEB (Lolth's realm, formerally Zanassu's realm; implied in Demihuman Deities)
LAYER 66: THE DEMONWEB PITS (Lolth's, Selvetarm's, and Keptolo's realm)
LAYER 67: HEAVING HILLS (Hezrou realm)
LAYER 68: UNNAMED (Void) (I)
LAYER 69: THE CRUSHING PLAIN (I)
LAYER 70: THE ICE FLOE (I)
LAYER 71: SPIRAC
LAYER 72: "DARKLIGHT" (I)
LAYER 73: THE WELLS OF DARKNESS (I)
LAYER 74: SMARAGD (Merrshaulk and Ramenos' realms)
Re: The Viper Pit (Sseth's realm; P&P)
Si: The Silent Temple (Planar Handbook)
LAYER 88: THE GAPING MAW (BRINE FLATS) (Demogorgon's realm)
LAYER 111: THE MIND OF EVIL (Realm of Sch’theraqpasstt; Dragon #151)
LAYER 113: THANATOS (THE BELLY OF DEATH)
LAYER 128: THE SLUGBED (Lupercio's realm; FoE)
LAYER 142: LIFEBANE (Chemosh's Realm, OHG)
LAYER 148: TORRENT (Planar Handbook Web Enhancement)
LAYER 176: HOLLOW'S HEART (Fraz-Urbluu's new realm; FoE)
LAYER 181: ROTTING PLAIN (Laogzed's realm)
LAYER 193: VULGAREA (Eshebala's realm; OHG)
LAYER 222: SHEDAKLAH (THE SLIME PITS) (I) (Jubilex's and Zuggtmoy's realms)
LAYER 223: RARANDRETH (OFFALMOUND) (Moander's realm; now Lolth's realm; F&A; OHG; DD)
LAYER 241: PALPITATIA (Grankhul's and Skiggaret's realms; OHG)
LAYER 245: OCEAN OF SCREAMS (Planar Handbook)
LAYER 248: THE HIDDEN LAYER (Eltab's domain; Champions of Ruin)
LAYER 274: DURAO (gateway layer)
LAYER 297: THE SIGHING CLIFFS (Lynkhab's realm; FoE)
LAYER 300: FENG-TU (Tou Mu and Lu Yueh's realm; 1e Manual of the Planes)
LAYER 303: SULFANORUM
LAYER 313: UNNAMED
Si: Illssender's Tower (Hellbound)
LAYER 333: THE BROKEN SCALE (Hiddukel's realm; OHG)
LAYER 334: UNNAMED (Eldanoth's realm; Faces of Evil)
LAYER 340: UNNAMED (A cold, desolate, voidlike place; Faction War)
LAYER 377: PLAINS OF GALLENSHU (armanite realm)
LAYER 399: WORM REALM (Urdlen's realm)
LAYER 400: WOEFUL ESCARAND (nalfeshnee realm)
LAYER 403: THE RAINLESS WASTE
IT: Mal Arundak, the City of Confusion (Fallen archon realm; FoE)
LAYER 421: SALTED WOUND (Realm of Doresain, the King of the Ghouls, vassal of Yeenoghu; Libris Mortis, name from the Mimir)
LAYER 422: THE SEEPING WOODS (Yeenoghu's realm)
LAYER 487: LAIR OF THE BEAST AND MANSION OF THE RAKE (Kanchelsis' realm; OHG)
LAYER 489: NOISOME VALE (Tarnhem's realm; deserted; Dungeon Builder's Guidebook)
LAYER 493: SLEEPLESS (Siragle's realm; Dungeon #28)
LAYER 499: CARRORISTO (Hellbound)
LAYER 503: TORREMOR (LAYER OF FLIES) (Pazrael's realm)
LAYER 507: OCCIPITUS (Shackled City)
LAYER 524: SHATTERSTONE (Vaprak's realm, OHG)
LAYER 531: VUDRA (Marilith realm, Dungeon #60)
LAYER 561: SHADDONON (Layer of Rhyxali, Princess of Shadow; Book of Vile Darkness web enhancement)
LAYER 566: SOULFREEZE (The Inner Planes Sourcebook)
LAYER 586: PRISON OF THE MAD GOD (Diinkarazan's realm)
LAYER 600: ENDLESS MAZE (Baphomet's and Pale Night's realm, OHG, FoE)
LAYER 601: CONFLAGRATUM (Alzrius' realm, Hellbound)
LAYER 643: CAVERNS OF THE SKULL (I) (Kali's realm)
LAYER 657: THE STEAMING FEN (Rod of Seven Parts)
LAYER 666: OPEN MAW (The Blood Wars trilogy; name by William Northern)
LAYER 672: RIFT OF CORROSION (3e DMG; Monte Cook)
There are other, unnumbered layers in
Throne of Bloodstone and the 1st and 3rd-edition Manuals of the Planes.
A popular misconception is that the layers of the Abyss are actually stacked on top of one another like a deck of cards. They aren't, as the poster map and descriptions of Abyssal layers in
Planes of Chaos made clear. The numbers represent only the order in which the layers were catalogued by the Fraternity of Order. The plane itself has no pattern to it, and while certain layers may branch off other layers, there is no objective way to say that one layer is the second and one is the third, as in the hierarchial structure of the Nine Hells. Most branch off from the first layer, the Plain of Infinite Portals, which sits in the center of all the other layers like a swollen spider in the middle of a complex and drug-addled web.
Most or all Abyssal layers are individually infinite in expanse (see, for example, the 1st edition Manual of the Planes, page 101)
besides, I thought it would be cool to just collect this stuff for the rest of us, as well. 
