The first two that come to mind are the Time Lost Protodrake and, finally, after several months, my favorite mount in the game, Aeonaxx. Oh how I love that drake. I won't be missing Deepholm that much though. Lol. I also enjoy collecting TCG pets but have not been able to afford any of those mounts yet. Perhaps the luck of the Irish will be with me and I'll win one. =)
Getting Arena Master In Wrath of the Lich King
When I convinced my husband to join a for the Horde Bear run. Despite losing the Raid Leader to some loopy bug when in the tram, and despite getting stuck on the Bronzebeard yet again. I convinced everyone everyone to hold tight and we killed the Dwarven Leader and my husband got his bear. He's a mount collector so it was the best thing I could ever help him get.
Count me in!
Greatest personal achievement was when I caught my Giraffe Calf. Felt like I searched forever to find one, and one day I finally found one walking around, it was so exciting to catch.
If I could have only one mount in WoW, it would have to be my Cenarion War Hippogryph. Since my early noob days of a lone night elf, taking flight on the back of a hippogryph fascinated me. When I took my first ride from Rut'theran Village to Darkshore, I was in awe of the majestic bird I was mounted on. Since that moment, I always desired to ride one all over the world. When flying mounts were finally introduced, I decided that the only flying mount for me was the Cenarion Hippogryph. Back in the day, it wasn't easy. I ran the Steam Vaults for reputation and would collect ears for D.E.H.T.A. while I waited for a group. It took some time, especially since people were caught up fighting the Lich King. At long last I gained exalted status with the Cenarion Expedition and gave up all of my gold for the bird of birds. As soon as I summoned the hippogryph, I was blown away by the 280% speed it was going at. Sure I could have gotten a swift gryphon instead, but having the hippogryph as my first epic flying mount felt special. I didn't even mind that it didn't have any standing animations but when 3.3 finally let it stand on it's feet, I loved it even more. I would spend minutes literally watching it just standing. The bird seemed to be full of life as it would look around and pluck something off the ground. Even today there are dragon mounts, phoenix mounts, serpent mounts and even other hippogryph mounts. But none of them compare to my love for the Cenarion Hippogryph. This is why it is my favorite accomplishment I have achieved in the game. Especially when it seems that not many have this mount, it makes me feel that this mount is only for me.
Getting exalted to get my netherwing drakes. That was a pain in the butt!
As far as achievements, getting rank 14 during old school vanilla PvP.As far as acquirements, it would probably have to be the Time-lost proto drake. I didn't end up getting him until towards the end of Cataclysm.
Leveling to 90 and getting the new mounts.
I can not choose a special achievement but I really like to get to level 90 every time I see him in my characters
I've got to say, when I got my Reins of the Phosphorescent Stone Drake, I was extremely happy. It took weeks and months of farming, but it was worth it. It is the only mount I use on my Shaman. Other than that, taming Skoll was second.I think a Tyrael would top it though.
Netherwing Drakes. This was the first big challenge I decided to face. As soon as I turned 85, I didn't gear, I didn't do anything, I just rushed back to the outlands and farmed those eggs like crazy. I was logging in during my fifteen minute breaks at work, during my lunch hour and even at 5AM, before heading to work just to see how many more had spawned so I could collect them. I realize now that the achievement wasn't hard, just time consuming. But as a noob, then, it was a big deal for me and I was so proud to fly around with my Malfas (Reins of the Purple Netherwing Drake).
Vial of the Sands
The thing I was most excited to get in WoW was the Twilight Drake. Wasn't expecting it; total epicwin moment. (=
The thing I was most happy/excited to receive was definitely my Dragonwrath, Tarecgosa's Rest.
Selling Challenge mode Boost to goldens, alliance side :P
Wish myself luck! :D
Obtaining the Skull of Gul'dan, so much lore in it. It is such a great feeling to carry the head of the greatest warlock in history around in my pocket.