Here's my top ten, for what its worth. For the most part I'm going to stay away from the obvious bands and choices, like Pink Floyd, Yes, Rush, King Crimson, etc. My first 2 choices are old standbys (artists) , but I think these albums are not well-known.
1. Goblin's Club - Tangerine Dream (not on the moon yet)
2. The Songs of Distant Earth- Mike Oldfield (not on the moon yet)
3. Oltre L'ignoto - Malibran
4. The Masquerade Overture - Pendragon
5. Variations of a Dream - Pineapple Thief (not on the moon yet)
6. Evolution of the Jazzraptor - Jack Foster iii
7. Heaven and Hell - Vangelis
8. Trying to Kiss the Sun - RPWL
9. Natural Timbre - Steve Howe
10. Any album by Niacin
Not about to say these are the best prog albums ever made, but I do think they are must haves for anyone looking for new and different music than regular artists.
Hope that helps tgleeson.
