I got a gold Welkynar motif book last year from combining fragments from Cloudrest.

TTC had no record of one being sold before and nobody I asked (checked in many guilds and friends did the same) had seen one before.

Of things currently dropping, I assume it'd have to be some of those Dwemer/Ayleid recipes going for 50 mil+ gold.

Of things no longer dropping...there're quite a few sets that are no longer in the game, such as the old dungeon sets - Physician, Ansur (rings and restor staff of Thorn), Destruction Suite (Ring of Embers, Ring of Blue Ice), Relics of the Rebellion (Necklace of Sardavar, Shield of the Man-Bull, Elf-Doom Maul), Earth Forge (Forge Master's Ring, The Ebon Sledge), Arms of Infernace (Flamedancer sword, Amulet of Conflagration), Arms of the Ancestors (Tenth Ring of Trinimac), old Hircine's which was named Saviour's and at some point was somehow BoE...there're also sets that used to drop off the dark anchors, such as the old Lich set (that came in the unique Lich stye featuring lich crown and all that) and some other sets I can't currently recall. It's not like they have any values other than not existing anymore, but I'd imagine still having them is quite rare XD These things were op rare even back then. They dropped in all the vet dungeons but with droprate lower than that of Aetherial Dust.

I gave the Lich items I had away (helped someone actually get a full Lich set and be like the only person on the server rocking it for years up til they actually introduced Lich set dropping properly lol), but I still have a full chest of the old sets I can't part with lol.




Oh! There's also an ice staff of nothing there, one of those bugged items that randomly dropped at some point - it features all the animations etc of ice staff...without actually having an ice staff. It's entirely invisible lol.

Aetherial dust, I have only ever found one of these and I do a lot of farming for mats. I have this list of suggested places you may find them Alik'r Desert, Auridon, Bal Foyen, Bangkorai, Betnikh, Bleakrock Isle, Coldharbour,
Cyrodiil, Deshaan, Eastmarch, Glenumbra, Grahtwood, Greenshade, Khenarthi's Roost, Malabal Tor,
Reaper's March, The Rift, Rivenspire, Shadowfen, Stonefalls, Stormhaven, Stros M'Kai but with the gazillions of nodes I have farmed they still don't drop for me. The one I found was up on the Alik'r Desert.

Holy necro thread... I think the rarest for me would have to be the aetheric cypher, which I got during the last anniversary event.

Got a bunch of 'old' crafting materials that seem fairly rare whenever I've looked

For me:
Perfected vMA firestick
Burning Spellweave firestick
Gold Imperial style books x3
Aetherial Dust x5
Aetheric Cipher (found in the wild), sold yesterday for 1m gold
Hot-Blooded Bantam Guar

Aetherial dust and some full motif books.