First of all...German Krautrock is really progressive (especially for it's time) and a must to check out. Probably my favorite of any of the progressive movements came from there. Check out Can (one of my favorites), Neu!, Faust, Ash Ra Tempel (another fav of mine), Amon Düül II, Popol Vuh... fuck, I could go on forever.
I'm too tired to really think of more/different ones right now. That should keep you busy for a few. Progressive is one of those really vague words though, could mean a lot of things and different sounds/styles.