Assuming you haven't checked them out already, Marillion's better albums would be more than worth tracking down, specifically "Misplaced Childhood", "Clutching at Straws", "Brave", and "Seasons End".
And I never miss an opportunity to plug Sieges Even, specifically their two most recent albums, "Sophisticated" and "Uneven". They'll be difficult to find, though.
Also, although they're more "power" than progressive per se, I heartily recommend Angra. "Holy Land" and "Rebirth" are both excellent, and their new album "Temple of Shadows" is simply fan-freaking-tastic. Far and away the best power/prog metal band working today IMO.