Dream Theater *this is a good list for people who are wondering where to start with these guys IMHO*
Best to worst in order:
Images & Words
Six Degrees Of Inner Turbulence
Awake
Falling Into Infinity
Octavarium
When Dream & Day Unite
Dream Theater
A Dramatic Turn Of Events
Black Clouds & Silver Linings
Systematic Chaos
Train Of Thought
Metropolis Pt. 2: Scenes from A Memory
People who don't know any better will tell you Metropolis Pt. 2 is their best album or that Train Of Thought is good cause its "heavier". Well Six Degrees is a better concept record than the former and a more dynamic record than the latter, so there.