I experienced something of a double whammy last night. I completed my 1,500th quest and I leveled to 80. I will always think of the night fondly, but I'm sure that I will also remember the particular quests I dinged on. For the 1,500 quests achievement it was a quest in the Love is in the Air chain out of Stormwind, Dangerous Love. I wasn't paying attention to my quest count so it was quite a surprise.
A little later in the evening I found myself chasing chickens in Sholazar Basin and then surfing a crockolisk past mutated undead Scourge. This time I was very aware of how close I was to leveling to 80. I thought it was going to happen turning in Pitch's remains, but it turned out that the quest that pushed me over the top was taking down a sandworm for a tribe of overmuscled, underbrained wolverines. Not exactly the most heroic of tales, but at least it wasn't for resorting to cheetah form to successfully capture the errant poultry.
Do you remember the quest or kill that marked a major milestone for you in the game? Let's hear it!