It can be anything from getting a mount you never thought you would ever get to a pet you had always wanted on a hunter to a quest that made you cry out in wonder and go...OMG.
For me it was this past Monday after I had asked on the WOW forums for help getting the Kor'kron War Wolf and a guild was generous enough to reply telling me leave my battle tag and be on that day at a certain time so they can take me to kill Garrosh and get my wolf. I logged on as usual had a raid earlier that day and got my Dragonslayer title was a great raid and all but the best was yet to come. As the time approached I was getting more antsy cause I had the leader on my battle tag and saw they were in the raid. Then came the moment when I got the invite and my heart skipped a beat I was going to get Wolfie. I zoned in and was like wow, it was the first time I was that deep in the raid only other time was doing the quest on Timeless so this was new to me. I came face to face with Garrosh and someone told me to use my death grip which was a joke but wanting to help carry my weight I did it was to say the least interesting though we wiped. Second time I again was bait meaning I didn't do anything except stand there and die and again we wiped. Third time I got to help hit him which was great it felt like I was earning Wolfie and not having him handed to me and so I hit him and hit him with all I got. Phase two came and that was where I died but I helped get them there all alive so they could finish him off and what a crazy fight it was as I watched Garrosh's health go down. Then came the moment of truth Garrosh fell to this guild and I saw on my screen the achievement, Ahead of the Curve Garrosh Hellscream 10 man and my thoughts were omg he is mine...Wolfie is finally mine. I thanked the guild so much that day for all their help in getting me this mount because I am not the best of raiders and loving wolves like I do made this mount more special. To this day Wolfie is in my mount bar and when I am running on Thunder and Timeless I am always on Wolfie even at the shrine you will find me running around on him exercising him. And so this is my WOW omg moment...the day Iowawolf got his Wolfie...