I'd love to know what you consider "progressive rock". Sgt Pepper is progressive rock's grandfather, that's for sure. I haven't heard The Beach Boys, but I read that their album "Pet Sounds" was one of the first albums that were described as progressive rock.

By the way, whether Pink Floyd hate being called progressive or not does not change what they do. If you check any rock music catalog, all of Pink Floyd's albums will most likely be labelled as progressive rock from Meddle onwards. Do you really think a "plain old rock" band plays songs like Echoes, On The Run, Sheep, Pigs, Shine On You Crazy Diamond, or Time? I beg to differ.

Edit, @silverpot: Words can not describe how much I love that song. :D The drums in it are the best ever.