Threshold is my favourite progressive metal band; such a shame Andrew McDermott gave up on them; albums like Hypothetical, Critical Mass, Subsurface are almost flawless, to me at least. 
other bands i often listen to - DT (especially the albums with Kevin Moore), Shadow Gallery, Circus Maximus, Riverside, Queensryche, Fates Warning, OSI, Redemption, Ark, Enchant, Psyco Drama, Thought Chamber, Sieges Even, Subsignal (from the ashes of Sieges Even), Psychotic Waltz/DeadSoul Tribe, Conception, Mindflow, Evergrey, Vanden plas, Dark Suns, Darkwater.
and i'm sure there are more...
