Dream Theater is probably the only band that brought most of us Bengali listeners into this particular genre or say they made this genre popular. But they're not the only ones as plenty of bands have been doing this rather complicated style of rock.The two bands who are considered to be the pioneers are Jethro Tull and King Crimson. Then there was YES and Rush. Some people even consider Pink Floyd to be a "Progressive" Psychedelic band. Many of u might oppose this thought. whatever....
Apart from the above, i like Ark very much...the drummer is simply insane. He's probably the 2nd best progressive rock drummer (the first being Mike Portnoy ofcourse). Then Shadow Gallery. Angra's pretty good as well.
I dont think Porcupine Tree falls into this genre as some one mentioned. They call themselves ART ROCK. You could call them a Psychedelic band as well but definitely not progressive.