This is a tough one. There are a few memories that stand out. Oddly enough getting my first character to lvl 60 back in Vanilla isn’t one, I don’t remember that at all.
I’m going to go with getting my first ever epic. It was on my hunter on Kul Tiras. I’d rolled there with friends and we’d made our own guild, but they left and as much as I liked the people left I wanted to raid. After meeting the GM during a UBRS run I ended up applying to Wowrush Rushers, and was accepted a few days later. Literally within minutes of my joining I was summoned to MC, to kill Ragnaros. Yeah, being dumped in the deep end is a thing for me. He was downed, and I ended up with the T2 legs on my first ever raid, and it all happened within 30 mins or so of joining.
Another great memory from that guild is the Christmas party we had once, where we had to race our characters naked and drunk from the far end of Winterspring to the Ashenvale end of Felwood. With Full Screen Glow turned on. Wish I still had screenies of that!
I stayed with the Rushers for quite a while, though there were periods I didn’t play, and I have some very fond memory’s of that guild and the people in it. Sadly our association did not end well, and whilst they still exist they don’t raid from what I have heard. I still look out for the in LFR but not seen anyone I know so far.