I like Prog music when it is dark, hard and sometimes heavy.

[evilB]

Welcome to the board musitron. SteveO has instructed that I should add to the list as we are the two who tend to bask in the dark proggy glory.
I would add:
Ihsahn (especially the album angL - Mike Akerfeldt makes a memorable appearance on the song Unhealer)
Pagan's Mind (The album Mind's Equation features an excellent cover of Bowie's Hallo Spaceboy)
O.S.I.
Kino
Katatonia (From Viva Emptiness on is more dark/doom than the older death metal albums)
Priestess (a little more hard rock but some proggy elements in there too)
Maschine
Spock's Beard
Scale The Summit
Intronaut
Animals as Leaders
Flower Kings
The Safety Fire
Big Elf (Money it's Pure Evil - kind of a snarly Beatles)
Theatre of Tragedy (I really like the Musique album)
Candlemass
Dark Tranquility - (more Death metal than others on this list not for those who need clean vocals)
The Gathering
Sleepytime Gorilla Museum (a very different band, they are an incredibly creative group but also requires the listener to be open to the unexpected)

So there's a few let me know which ones you liked and I'll try to recommend more similar to them.