I have reposted it here with some minor spelling corrections, additional clarifying text, headings, and navigation.
Updated to add Shadows of the Hist, Horns of the Reach, Clockwork City, Morrowind, Summerset, and Events.
- Base Game
- Golden Saint – unlocked at rank CP20
- Dark Seducer – unlocked at rank CP60
- Mannimarco – unlocked at rank CP100
- Imperial Chancellor – unlocked at rank CP160
- Caldwell’s Helm of Heroism – complete Caldwell’s Gold (obtained at the Harborage from Cadwell after the completion of the main quest and the silver portion of Cadwell’s Almanac)
- Skeleton Polymorph – Complete ‘The Bargain’s End,’ a quest found in the NW of Shadowfen
- Emperor’s Regalia – Become Emperor (Cyrodil / PvP)
- Xivkyn Auger, Dreadguard, and Tormentor – Buy Tel Var lockboxes. They’re tradeable, which is why it’s listed here.
- There’s also the 4 horses you can buy from any stablemaster.
- There are various Momentos you can obtain by completing the quests found in Public Dungeons. (15)
- There is one obtained by meeting Almalexia through the Deshaan questline, as well as one obtained by doing the Shad Astula questline. (northern Deshaan)
- There was one that was free, during the second anniversary event, but it is no longer available. Finally, there is one obtainable by completing a quest in northern Cyrodil.
- Imgakin Monkey – Play during the beta. No longer available
- Razak’s Opus – Complete the Razak’s Wheel Public Dungeon
- Bristlegut Pig – Visit the ESO booth at PAX, and other gaming conventions. Or, buy a code in-game – people will sell some every now and then.
- Soul Shriven Skin – Small chance to get it while playing in IC
- Stonefire Scamp – Same as above
- Necrotic Hoarver – Complete Imperial Challenger achievement
- Echalette pet – Visit Wrothgar
- Vosh Rakh Ceremonial Mask – acquired during the main quest
- Regalia of the Orsimer King – Complete the main quest
- Old Orsinium Sentry – Fill the Orsimer House of Glories Trinimac’s Penitent Knight – Same as above
- Hidden Pressure Vent – Complete Rinkadleft
- Malacath’s Wrathful Flame – Complete Old Orsinium
- Maelstrom Baron – Complete veteran Maelstrom Arena
- Jackal pet – Visit Hew’s Bane
- Thieves Guild Leathers – Join the Thieves Guild
- Merchant Lord’s Formal Regalia – Acquired during the main quest
- Pirharri the Smuggler assistant – Complete the main quest
- Coin of Illusory Riches – Become a Master Thief
- Drom’Athra Skin – Complete vet Maw of Lorkhaj
- Assassin Personality – Visit The Gold Coast
- Shrouded Armor – Acquired during the main quest
- Black Hand Robe – Beat the Main Quest
- Cadaverous Assassin – Complete the Litany of Blood Achievement
- Blade of the Blood Oath – Complete the Bane of the Gold Coast Achievement
- Box of Forbidden Relics – Complete the Flawless Sacrament Achievement
Shadows of the Hist:
- Spiderkith: Cradle of Shadows Challenger Achievement
- Amber Plasm Skin Daub: Ruins of Mazzatun Challenger achievement.
Horns of the Reach:
- Bull Horns Emote: A new collectible emote obtained by entering either dungeon in Horns of the Reach.
- Collectible Furnishings: A new displayable trophy and bust from each dungeon, obtained by defeating Domihaus the Bloody Horned in Falkreath Hold and the Earthgore Amalgam in Bloodroot Forge in Normal and Veteran modes.
- Dreadhorn Shaman Skin: Obtained by completing the Falkreath Hold Challenger achievement.
- Keptu-Horn Skull Sallet: Obtained by completing the Bloodroot Forge Challenger achievement
- Clockwork Obscuros – Complete the Clockwork City prologue quest “Of Knives and Long Shadows” available in any Mages’ guild and finding a note titled “Order of the Eye Dispatch”.
- Scintillant Dovah-Fly: This non-combat pet will join you when you first set foot in the Brass Fortress.
- Begone!: Obtain this Emote by completing the quest “Lost in the Gloam” in Clockwork City.
- Umbral Projector: This Memento is acquired by completing the achievement, the Hero of Clockwork City.
- Revolving Celestiodrome: This unique Furnishing is obtained by completing the quest “The Light of Knowledge” in Clockwork City.
- Trophy, Saint Olms the Just: This Furnishing is obtained by defeating St. Olms in Asylum Sanctorium on any difficulty.
- Bust, Saint Olms the Just: This Furnishing is obtained by defeating St. Olms in Asylum Sanctorium on Veteran difficulty.
- Sanctified Silver: This Skin is available from defeating St. Olms in Asylum Sanctorium with his allies in the same battle, on Veteran mode.
- Clockwork Curator: This Polymorph is rarely available as a Runebox, dropped from defeating St. Olms in Asylum Sanctorium with his allies in the same battle, on Veteran mode.
- Regalia of the Scarlet Judge: The famed vigilante known as the Scarlet Judge has upheld justice in Morrowind for generations, and has most recently been spotted near the town of Suran.
- Sixth House Robe: Officially, there is no Sixth House, and these robes do not exist. Unofficially, Sixth House cultists in the Forgotten Wastes have been identified with fragments of these ancient robes in their possession. If one were to acquire all seven pieces, they might be able to reform them into an intact garment. What would such a relic be worth, to the right person?
- Vvardenfell Scale Model: Librarian Bradyn in Vivec City believes that completing such a model will reveal the location of the lost Library of Andule, an ancient repository of the knowledge of the Great Houses.
- Assembly General (Trophy): Complete the Halls of Fabrication to bring home the head of this brazen behemoth.
- Assembly General (Bust): Complete the Halls of Fabrication on Veteran difficulty to earn this tasteful bust of the Assembly General.
- Head & Body Markings
- Morag Tong Face & Body Tattoos: Assist Naryu Virian and the Morag Tong in and around Balmora to earn the right to display these striking tattoos.
- Buoyant Armiger Body Tattoos: Be named Champion of Vivec to earn the right to wear the body tattoos of a Buoyant Armiger. (Divine Quest line)
- Neramo’s Lightning Stick: Aid the artificer Neramo in the Dwarven ruins of Nchuleftingth to earn this shocking memento.
- Dreamer’s Chime: Complete the quest “Echoes of a Fallen House” in the Forgotten Wastes public dungeon to recover this haunting bell.
- Replica Tonal Inverter: Designed to temporarily disrupt the flow of energy in magical devices, help invent the device this replica is based on in your quest to aid Vivec.
- Telvanni Magister: Assist an Argonian slave in her meteoric rise through the ranks of House Telvanni, and learn to adopt the mannerisms of a Telvanni Magister. (Sadrith Mora)
- Dwemer Theodolite: Sentries such as this one may have once been used to survey subterranean areas, and were likely involved in the construction of Nchuleftingth. It is theorized that some of the guardian constructs in this public dungeon may contain repurposed parts from defunct Theodolites, though finding a functional part would be a challenge for even a seasoned adventurer. With all seven parts, the mechanism could be reconstructed. Whether kept as a loyal pet or sold to the highest bidder, such a device would be sure to draw attention.
- Fabrication Sheath: Proudly display your victory from Veteran Halls of Fabrication with this body sheath of burnished bronze!
- Public Dungeons
- The Big-Eared Ginger Kitten Pet is earned by finding the seven Runebox Fragments containing its collar, sleeping-basket, milk saucer, and other necessities from the Karnwasten Public Dungeon, and combining them into a Runebox.
- The Sea Sload Dorsal Fin Memento is obtained by completing the quest “An Unexpected Betrayal” in the Karnwasten Public Dungeon.
- The Psijic Glowglobe Emote is earned by finding its seven Runebox Fragments from the Sunhold Public Dungeon, and combining them into a Runebox.
- The Gryphon Feather Talisman Memento is obtained by completing the quest “Sunhold Sundered” in the Sunhold Public Dungeon.
- The Collectible Trophy of Z’Maja is obtained for completing the new Cloudrest Trial on any difficulty.
- The Collectible Bust of Z’Maja is obtained for completing the new Cloudrest Trial on Veteran difficulty.
- The Z’Maja’s Shadow Skin is obtained by completing the new Cloudrest Trial achievement, Cloudrest Vanquisher, on Veteran Hard Mode.
- The Psijic Skullcap Hat is earned by completing the quest “The Towers’ Fall”, in Summerset.
- The Face Imprint of the Psijic Order, a Face Markings collectible, is obtained by completing the quest “The Shattered Staff”, in Summerset.
- The Body Imprint of the Psijic Order, a Body Markings collectible, is earned by completing the quest “The Towers’ Remains” in Summerset.
- The Mystic Eye Psijic Cuirass, an Outfit Style, is obtained by completing the quest “The Crystal Tower”, in Summerset.
- The Psijic Warden Gauntlets, an Outfit Style, is obtained by completing the quest “Lost in Translation”, in Summerset.
- The Fan of False-Face, a Collectible Furnishing, is obtained by completing the Relics of Summerset achievement.
- Hollowjack Spectre Mask: Witches Festival
- Midyear Victor’s Laurel Wreath: Midyear Mayhem, Star-Made Knight achievement
- Free Costumes, canopus12, Reddit