Concept albums (top 5)

obviously, the 2 opeth concepts.

and also:

pink floyd - the wall
pain of salvation - everything by them [they always make concepts]
dream theater - scenes from a memory
 
Opeth - Still Life
Opeth - MAYH
Emperor - Prometheus
Dream Theater - Scenes from a Memory
Dream Theater - Six Degrees of Inner Turbulence (laugh if you want, but I thought it was a pretty good album)