Aaron Copland - Symphony #3
The Gourishankar-2nd Hands
The Who-A Quick One
The Who-The Who Sell Out
Elton John-Goodbye Yellow Brick Road

I know there's not a lot of prog as such (apart from 2nd Hands) in there but there are some prog feels to tracks on all the other albums (even the Copland as the 4th Movement quotes from his "Fanfare for the Common Man" and we all know what ELP did with that )