I'll definitely echo Rush with PEW/MP, but also AFTK/HEMI as well. That whole group of four albums are pretty great IMO.
As for DT, I'd probably pick SFAM/SDOIT over IAW/Awake, but both are great. And I'd probably also throw in DOT/AVFTTOTW.
As for other bands, I'll offer up:
Big Big Train - English Electric Part One, English Electric Part Two
Spock's Beard - V, Snow
Transatlantic - Bridge Across Forever, The Whirlwind
Porcupine Tree - In Absentia, Deadwing
Liquid Tension Experiment - LTE, LTE 2 (is this cheating?
)
Kansas - Leftoverture, Point Of Know Return
Pink Floyd - The Dark Side Of The Moon, Wish You Were Here
Queen - Queen II, Sheer Heart Attack
Genesis - A Trick Of The Tail, Wind And Wuthering
Yes - Fragile, Close To The Edge
I'm sure there's dozens more I could put but these were just some off the top of my head.
-Marc.