I would highly recommend any and all of Christian Eichhorn's Mörk Borg supplements - they all have fantastic layout and art, creative content that adds new systems and creative twists on existing ones, and capture the brutal and beautiful feel of the core book.
Apocrypha is a must-have if you're looking to add kinds of new systems and encounters to your session, offering perhaps the most wide variety of system supplements of Christian's collection. Apocrypha includes a multitude of new skills and statuses, revival mechanics, and fresh encounters like "The Body Shop" for character augmentations, the "Forbidden Vault" for all manner of evil items, and "The Hunter's Guild" for "Hirelings" (followers) and a bounty exploration system. You'll also find new classes, a variety of monsters, and d86 'Otherworldly Summons' and two small dungeon crawls for some additional fun.
Enjoy Apocrypha? Check out Purgatory for even more unique gamplay supplements/additions. Want something to complement Apocrypha? Check out Galgenbeck Sacrifice or Bergen Chrypt for a more campaign-focused adventure.