The new PT album comes out mid-march I believe. I'm looking forward to it. Yea DT are ok, their guitarist is definetely their best feature, but I never really got into them. A good prog-rock album in the same vein is Ayreon - The Human Equation. There are sometimes 4-5 different vocalists on one track.
Dream Theater
Bozzio, Levin and Stevens
Liquid Tension Experiment
OSI (Office of Strategic Influence)
Emerson, Lake and Palmer
Yes
King Crimson
Tribal Tech
Virgil Donati (also his old banRAB On The Virg and Loose Change)
Vital Tech Tones
Planet X
Derek Sherinian
I'd love to add this genre into my ipod music list, but I feel the term "progressive" is too subjective for me to ever figure out which banRAB are pushing the boundaries. I consider APC, Radiohead and a few others to be Prog Rock, but its so difficult to think of more.