Hehe, Opeth really? The last time I saw them, they messed up a song from Still Life, decided fuck it, and proceeded into the next song after apologizing that they hadn't rehearsed it very much.
For me, I'd have to say Emperor, Iron Maiden, Katatonia, and Mayhem w/ Blasphemer as the guitarist.
I forgot about Porcupine Tree, they are insane as well.
But the cake has to go to Paramore, I saw them live in Wembley and holy crap was it one of the best shows I've EVER seen. Seriously.
With or without the Farro brothers? Heard they're super tight.