Probably would say getting lucky enough to get the Eye of Sulfuras and the right binding of the windseeker which got me both legendaries in the same run.
Azure Whelpling pet.
Getting my loremaster achievement! Took me forever.
Getting the Sgt. Major title on my druid
I would have to say obtaining Experiment 12-B from Ultraxion, however let's leave out the fact that I spent all my gold buying it from the winner :D
Congratulations to whoever wins, especially if it's me!
The most excited I've ever been was when I obtained my Albino Drake. It was before WotLK even hitted the live servers, the day after achievments were introduced into the game. I knew the achievment was in so I started working on it and I hitted exalted with Kurenai the day after the patch, bought the talbuks and wham, there was that awesome first drake I ever owned. Awesome to just sit in Shattrath and have people commenting and liking your drake ^^.
Winning the Kalu'ak Fishing Derby to get my "Salty" title.
First time I saw a feldrake I just had to have it. Also it will help me reach my goal of 100 mounts.
As simple as it may seem it was getting to the point (Gearwise 425) to use the Scenario setting ,this by far is my favorite thing in the game I have played on and off since BC and one of the thing I didn't like was not being able to play and get the higher end gear without being in a raiding guild or running dungeons nonstop for hours on end. After the first few Qs I got some Epic wrist (476) that I could use, not the best in the game but a great start and got me looking forward to more runs where the pressure is minimal and the reward great .Thank You Blizz for this nice add in MoP.
Taking my first misty breath of fresh Pandaren sea air was a feeling matched only by my less recent descent into the hellfire of Deathwing's twilight retreat, returning to the surface of Azeroth with Ti'thak, Steps of Time at my side. For the Horde!
Title rewarard the exalted and light of elune.
I'm most excited to achieve the "Zookeeper" title!
Visiting old content that has naturally been left behind, content which I never had time to commit to while it was the new content.
The most exciting achievment for me is being able to play this wonderful interactive game. Meeting new poeple across the world. This keep my mind of from missing my family because work call me away from them and i get to play with my son at night and talk to see how things are going.
Getting my Magic Rooster, I used to stare at people riding it until they were too far to follow.
I'm still trying to get the Stratholme mount.. after all these years... will be super-excited if it ever drops for me lol
Finally getting Val'anyr
Downing heroic Deathwing... after Cata was over. lol
I would have to say assembling Val'anyr. It was my first legendary, and I was honored that my guild chose me as its first recipient.