Halls Of Reflection , it was epic when you stand against Lich King with Sylvanas, ready to die.
I WOULD say my favorite instance would be 6.2's upcoming Hellfire Citadel, but since I don't know if that counts, I'll go and say the classic IceCrown Citadel! =p
My favorite instance is probably the old version of Scholomance. The whole place felt awesome to explore.
My favorite instance has to be Karazhan. The music, the random event, the spooky feeling of it all...
Tough call, as WoW has had so many good ones over the years. That said, think I'd have to go with Old Deadmines. The boss voices for that dungeon were so great, and very little has been able to live up to it. (Putricide in ICC comes awfully close, though!)
The Vortex Pinnacle, followed by Throne of the Tides ;p
Scholomance! Old and new, I love creepy places n_n
Throne of Thunder was just an amazing raid!
My favorite instance in World of Warcraft goes to the Vanilla version of the Sunken Temple. Just the amount of stuff in that dungeon....from the basement puzzle to the Dragon's Call off of Shade of Eranikus being my first epic on my rogue.
I enjoy running dungeons, but my favorite instance is Karazhan.
I like Karazhan for its story and layout.
Mogu'shan Vaults, because it has Will of the Emperor.
I simply adore KarazhanNo matter how much fun you have in any other instance, it will never be "I'm fighting The Big Bad Wolf" fun *-*
Throne of Thunder.
My favorite instance is definitely Stratholme....We used to run this over and over again trying to get the mount and different set pieces. I love that place.
My favorite instance is Gate of the setting sun :)
The Vortex Pinnacle, this dungeon's music is awesome :)
My favorite instance is the Black Temple! It's so vast and amazing!