Blame!
Blame! is a 10 volume post-post-post-apocalyptic cyberpunk manga by Tsutomu Nihei. It follows the adventures of Killy, a man of few words and even fewer expressions, as he wanders a series of immeasurably vast superstructures known collectively as "The City". To aid him on his quest is his trusty gun, the eponymous Gravitational Beam Emitter (a weapon so potentially powerful it could make Exterminatus look like a wet fart) and Cibo, his seven foot albino scientist partner(who happens to be a gurl, who turns into an overpowered 7 foot anorexic robot who turns into an anorexic cyber demon loli). Their goal is to find something called the "Net Terminal Genes" in order to... do something, for some reason... It's all very vague, and reading through more than once will most likely be necessary.
The series is best known for it's unique style, art and subject, as well as being notably and unapologetically grimdark. This, combined with the fact that it lacks most of the stereotypical elements that put some people off manga, has endeared the series to a lot of fa/tg/uys.
Cyber Dungeon, a fanmade RPG is currently under construction at RPGnet. http://wiki.rpg.net/index.php/Cyber-Dungeon_Index Since this is still only skeletal fluff after two years /tg/ has now taken the initiative. Blame! the RPG is a go. http://www.suptg.thisisnotatrueending.com/archive.html?tags=BLAM