I've started typing my list for this thread like, seven times. I keep getting halfway through it and then second-guessing myself and giving up. So, this time I'm going to finish. And it's not going to be perfect, but, my opinion is something like this:
Tier One: Images and Words
Tier Two: Train of Thought, Scenes from a Memory (and I know it's still early, but I'm tentatively putting ADTOE here)
Tier Three: Awake, Six Degrees of Inner Turbulence, Black Clouds and Silver Linings
Tier Four: Octavarium, Systematic Chaos, Falling Into Infinity
Tier Five: When Dream and Day Unite
And for the record, I still enjoy WDADU.