Pink Floyd of course. So many good groups though, Zeppelin, The Who, Sabbath, Allman Brothers, it goes on.
But Progressive Rock, like Floyd, King Crimson, Yes, Rush, Jethro Tull, thats the best music to listen to while youre high. It's so damn complex and intense. If you want to know what progressive rock is, check out the album Fragile by Yes, one of the greatest albums ever made.