I have everything by Pelican. In some ways, the original EP (on which "Mammoth" appears) is best. Heaviest, anyway. The new album is quite good. A bit more of a "post-rock" element. "March Into the Sea" is one of the best tracks, and the long version on the EP is worth getting.
Isis has a similar sound, with some vocals. Panopticon and Oceanic are both good.
Definitely check out Jesu, Justin Broadrick's current project (i.e. after Godflesh).
Also don't miss the new Earth album: Hex, or Printing in the Infernal Method.