Transatlantic and The Tangent aren't exactly old school, but IMO they're among the best in the genre.
I also love Styx (who are the best in the genre), (arguably) Queen, Yes, Rush, Kansas, and King Crimson.
Kansas and Kerry Livgren's Christian albums such as Seeds of Change are amazing. Anyone who does not have this album needs to get it right away
Here are two songs from that album:
I don't listen much to classic progressive rock.
But I have Neal Morse's "Testimony" and the Flagship album, Christian Liljegren released in 2005 (with C.J. Grimmark on guitar):
Another prog rock album I have is Revelation Project:
Heard of em, but never listened to any of their stuff. I think it would be awesome to tell people about though - "Don't tell me you've never heard of Van Der Graaf Generator!"