Deicide

Honestly, I'd suggest the rest of their discography, though you may want to go for In Torment In Hell dead last. The rest of the discs are decent in their own right, and even I.T.I.H. has it's moments in spite of simplicity in song writing and shit production. For the very next purchase, hit up Serpents, Scars, or Once.
 
I have Serpents of the Light, and i thoroughly enjoyed it from the first track till the last track.