Karazhan. I tanked, but, BOY, did I screw up back then... x) Hopefully I got better since those times.
My old guild kept on losing people so it was hard to do MC. We rocked AQ20 and ZG20 till expansion. That was my first raid(s)
Not to mention I was almost 98% was the one that got transform into Little Red Riding Hood during Big Bad Wolf.
Was just about to say that dps couldn't be true, but I read it as Naxx at level 60. xP
But when you mention it, I remember doing Sartharion in a PUG and wondering what was wrong with the members who where pulling less than 2k dps at launch. :P
OT: I'm hesitant to call UBRS my first raid (though with todays standard it would be). Getting carried through that instance with the help of my friend's guild, and accidentally pulling the last boss as I didn't see him around the corner. The chat lit up with people saying "stop!" and "careful!", and I only thought they were trying to tell me to get out of shit. So I backpedaled and body pulled him. They weren't happy.
I think my first raid was Zul'Gurub, considering what was thought of as a raid back then. But it must be a close contender with Molten Core.
UBRS (when it was a raid)
UBRS and MC, my Shaman dinged 60 in ZG.
scholo. I remember dropping group before the boss died or to pick up the deeds to get quest credit. We raided everything back when.
Technically Molten Core. Had no idea what the fuck I was doing, my friend let me mess about on his account. I didn't care, I could hit a button and make lighting go so it was all good!
Properly raided though... would have to be Naxx 2.0. Yes, I'm strictly speaking a Wrath baby. Whilst I leveled through Vanilla and BC I didn't do endgame stuff until Lich King.
If we are talking live, then UBRS. But guess Molten Core count as first real Raid.
I did do some crazy Onyxia shinanigans in Beta though, before there even was a 40man cap on raids. Was some crazy zerg with lowbies :}
Never interrupt your enemy when he is making a mistake
Molten Core, i believe I was still level 58 at the time, but it barely mattered because we were 40 people just jamming our face into the raid hoping for the best. It was essentially the experience we got in the recent anniversary.
Deadmines with, if IRC was with about 10 people.
-Not strong enough to do it instance mode? Let's raid it!
MC. But it wasn't really to raid per say. The best guild on the server would bring in pugs to farm the trash over and over thoughout the week for the materials to make FR gear. The pugs would get the BOE epics they no longer needed. But it was the first toe in.