My warrior's Halberd of Smiting, especially since it's not obtainable anymore.
Not directly. Attunement to Naxx was based on your rep with Argent Dawn. Exalted was free, anything less was a combination of gold and various items such as Righteous Orbs. The argent dawn commendations when worn let you collect scourge stones which could be turned in for rep. You got them for killing any undead mob in WPL/EPL of from trash and bosses in Stratholme.
My name is Cernunnos, I will love you like no other, I have died a thousand deaths, each time I died I thought of you.
My Very Light Sabre. It is an elegant weapon, for a more civilized age.
Diary of Weavil (best in-game book read...too funny!)
Scepter of the Shifting Sands
Item I still wish I had: Enamelled Disc of Mojo I guess I could go farm the look-alike on the Isle of Thunder, but who knows how long that'd take?!?
A lot of things, old things, things you cant get anymore or just those that hold a special place in my heart. Old keys, the item that allowed for the collction of Sillithid carpace (since it was my guild that opened the Gates of Ahn'Qiraj on Shadowsong EU), and other stuff.
But obviously, the biggest one of those items would be my Corrupted Ashbringer.
Looking marvelous in velvet.
I am very economical on my Path of Illidan, Path of Cenarius, Sandbox Tiger and Party G.R.E.N.A.D.E.. I really love those vanity stuff!
And i am never deleting my Blackhand Doomsaw as it is the best weapon an orc can wield!
My Scepter of the Shifting Sands.
I'm pretty attached to my rogue's Pet Rock and to my Paladin's Arcanite Ripper. I got the Ripper like this and never let my friend forget it:
My all-time favorite part of WoW was in TBC due to the awesome guild I was in, and I only have 1 item left from around that time, and that is one item I'll never sell. Stormherald!
Cave Cave Deus Videt
The Skull of Gul'dan on my warlock. It really made me feel like a true warlock
During my first few days playing, it was the Lunar Festival.
I ended up with some Festival Dumplings. Noticing they were for a percentage of HP and Mana, rather than a fixed amount, I decided to save these rare and overpowered treasures until I was of a high enough level to make good use of them. I mean, you never know when you might need health and mana, right?
I promptly forgot about them, until I found them the other week. I haven't the heart to eat them. Plus, they're about 8 years old at this point. That's older than some WoW players are in real life...
The items for the Dreadstead quest, and a few pieces from the Wrath launch event. I also keep Nibelung, for the fond memories. I was the first in my guild to get it, and the proc rate was amazing for warlocks.