Legendary quality Ebony Mail, valued at 18,333 Septims. Turns out I was wearing it the whole time

Yes I had over 500 books stored in a dresser (saving them until I get several full sets to display on shelves) and I put one too many in them and part of the collection disappeared I guess. Not valuable ones as far as I know though

Jordis the sword maiden wearing Legendary Enchanted Daedric Armor and MY GD Ebony Blade(DAEDRIC WEAPON) somewhere near Frostmeyer Cave after a dungeon quest....

J'Zargo and the Red Eagle sword I'd equipped him with in Broken tower redoubt. He was limping badly, and I went thru a load screen door expecting him to follow me but he didn't. I went back thru the door and he'd gone.

I've lost my Notched Pickaxe, Daedric Warhammer and my wife.

Red Eagle's Bane/Fury is re-obtainable

Maybe not the most valuable, but I lost the Coral Dragon Claw for a while. I was standing in front of the door that needed the claw, checked my inventory, and what.... where is it? I had three houses at the time and had to look all over the place. Couldn't find it. Man, I then had to retrace through the followers I had had. Finally found it in Onmund's inventory. Wow. Took a long time to find it. I was woried I had sold it.

After endless hours of skyrim I lost the most valuable belonging, my life. I now have no life, the waking moments that aren't spent at work, are spent button mashing, washing the cheeto remnants my controller, and microwaving a hot pocket.

I sold the ebony blade mistaking it for some random ebony sword.

Dragonsbane, my first Scimitar, and a Blades Sword. First two lost when fighting a named drugr who constantly used Disarm (I forget who, I remember he was near Ivarstead and he would clone himself though). I lost the Blades sword accidentally when I was Overencumbered and I dropped it. However, I found it when I was doing Boethiah's Quest.

I lost Stormbreaker, the lightning sword that I crafted myself. It was my favorite weapon.... Nothing will replace it. Some Draugr shout disarmed me and it fell through the map.

The Blades sword isn't a scimitar, it's a Katana.

A legendary daedric mace that did 156 points of elemental damage. A Draugr disarmed me and it glitched through a wall.

Dragonbane. Accidentally sold to a shopkeeper when the inventory list jumped up on me. Decided it wasn't worth buying back for what he was charging.

I thought I had lost the Skull of Corruption from the weapon plaque in the basemant of Honeyside. I had had the same problem with the Ebony Blade but it had just fallen to the floor beneath. The staff wasn't there though. Eventually I found it in a different spot on the floor. So I've learned not to try to put something on the middle weapon plaque in the enchanting room. The top and bottom one seem to be fine, though. Go figure.

I've lost 3 followers as a mage, but I think chain lightning has to do with it...