Porcupine Tree are amazing.

Opeth, definately Opeth in Montreal. I had been following the band for quite a while, they were better live then anything I ever saw before or since. They made everyone else who performed that night look like utter amateurs.

Second would have to be Porcupine Tree. It was simply stellar.

Third was Air. They were utter dicks though and wouldn't even acknowledge that there was an audience that they were playing for. But other then that the music was really good.

And finally the first band I ever saw, Primus, it was just utter insanity. First mosh pit.

I just love this band and this song.

Porcupine Tree is an English progressive rock band formed in Hemel Hempstead, Hertfordshire, England by Steven Wilson. Their music is a combination of rock, psychedelia, ambient and, more recently, metal. The main songwriter, Wilson, once commented: "I like so many different types of things, and they all go into the melting pot, if you like, that produces the music of Porcupine Tree."

- More @ Wikipedia

I would turn into Moonloop by Porcupine Tree. But I remember this one.