So, this is a very tough one as I have A LOT of great memories. I will just list some of them.
Probably the best is when I got my wife (then GF) to get into the game. Now she really enjoys it. Then....well she hated it. It was one of our biggest issues of contention. Fights and fights over playing the game. Now we play together and it makes things much better.
I have three other outstanding memories in WoW to share.
1) My first guild: This was a random little guild called the Red Dragon Clan. We formed up and had a celebration on the edge of the Loch in Loch Modan. We shot red fireworks and we were provided with out first ever tabards. This was my first real taste of community in an MMO. I ran around kicking the crap out of stuff. I joined out guild leader in a zone I had no business being in (I think it was Burning Steppes) when I was in my 30s or 40s. I mucked around noob style and had a great time of it.
2) My first REAL guild: This was the guild that I joined and spent the next several years in. I joined House IIMKI at the end of Vanilla and we ran instances every day. This is where I learned to tank. I have friends from that guild to this day. We went into BC and eventually, everyone was kicked out for some stupid ass loot bullshit. We reformed in a guild called Reborn and became a very decent raiding guild on our server. It finally broke up for good towards the beggining of Wrath as everyone jumped ship to raiding guilds. I was one of the last to leave. That split was possibly one of my saddest.
3) Saturday Night Karazhan: This was one of my favorite times in WoW, and it was certainly my favorite raid. I led a Kara run every single week. We got friends together and plowed through it. It would take two sessions to get through it when we first started. Towards the end, we were blasting through in under 2 hours. We took all of our alts in there and had some very fun times. This was also some of my good friends first taste of raiding. I miss Saturday Night Kara.
So, those are some of my good memories in WoW.