I Think that was really a good idea (sorry my language, I am not an english speaker...) include some bands that are not progressive in your essence under the titles like "prog roots" or "prog influenced" or, maybe, "prog moments". In fact, we can discover a lot of lost and excellent music that must be classified as progressive! If we look toward 70`s...then...can find some gems. I remenber some songs performed by bands like Led Zeppelin, Deep Purple, The Who, Jeff Beck, Allman Brothers Band, etc.
I don´t understand why the brazilian band of late 70´s/early 80`s called 14 Bis are not included in this site (I from Brasil, yes). Some song of them, like a wonderful "As Quatro Estações de Vega", is a trully masterpiece of brazilian prog rock! 14 Bis is a "son" of the famous (for us, at least) band "OTerço" and have a good mix of prog/folk/pop music.