Info dump tiem! From an HTML file I have sitting on my hard drive indexing a collection of Seinen. Selected entries follow, descriptions are in spoiler tags to save visual space.
I disclaim any association between me and these series. I have this file because I'm a massive info collector, I haven't read most of these series. I filtered on the basis of standard western male interests with a little bit of weird. I doubt you want to be told about a slice of life manga that isn't available in English and revolves around a robot that owns a cafe in the countryside.
Nijigahara Holograph by Inio Asano
I am rather interested in this, but I've yet to read it.
[ Spoiler ]
Suzuki is a troubled boy. He's lived with uncaring foster parents for most of his life, alienated from the other kids at his school, owner of a cynical, unhappy mentality. Komatsuzaki is a violent, unpredictable bully whose head trauma causes him to act in mysterious, inexplicable ways. Arakawa is a no-nonsense, normal girl who pines after Komatsuzaki but can never have him. A teacher with just one working eye. A mother who committed suicide. A daughter in an endless coma. Attempted rapes, murders, extortion, sexual deviance, and a freakish explosion in the butterfly population. All of these elements are whirled together in a story spanning 10 years, a tale of blackness, pain and apocalypse. And maybe just a bit of hope and redemption.
Eden by Hiroki Endo
I've read a few chapters and want to read more. That is to say, I actually reccomend this on the basis of what little I've read.
[ Spoiler ]
In the panic surrounding a worldwide pandemic which kills 15 percent of the population and cripples many more, a secret organization, Propatria, topples the UN and seizes control of much of the world. A boy and a girl, raised in an abandoned virology research center, immune to the virus, are attacked by the Propater and escape. 20 years later the boy is the most powerful drug lord in South America. The rest of the series follows the couple's son as he makes his way through the harsh new world and his relationships with various militant factions, drug lords and prostitutes. Based strongly on Gnostic mythology, all major characters are named after gnostic deities, and have analogous roles. This manga bears a strong resemblance other Japanese distopic sci-fi like Akira, Ghost in the Shell and Evangeleon. While Endo is heavily influenced by these works, Eden stands on its own with its strong characterization, international scope and well-considered political and economic realism.
Strain by Ryoichi Ikegami
I've read a few chapters, but I don't think it's on top of my list of things to read. Certainly below Blade of the Immortal.
[ Spoiler ]
Mayo is a professional assassin who never asks for more than 5 dollars per kill. He is hired by the "Organization" to kill the mother of a young prostitute, Shion. Shion pleads with Mayo, and convinces him to give up on his mission. As Mayo takes pity on Shion and her Mother, the leaders of the Organization pronounce a death sentence on him.
Vagabond by Takehiko Inoue
I've always been suggested this by various groups. Apparently it's pretty similar in tone to Blade of the Immortal, but it seems it's older.
[ Spoiler ]
Shinmen Takezo is destined to become the legendary sword-saint, Miyamoto Musashi--perhaps the most renowned samurai of all time. For now, Takezo is a cold-hearted killer, who will take on anyone in mortal combat to make a name for himself. This is the journey of a wild young brute who strives to reach enlightenment by way of the sword--fighting on the edge of death. Winner of the Kodansha Manga Award in 2000 and an Osamu Tezuka Culture Award in 2002
Parasyte by Hitoshi Iwaaki
Mostly echoing Akira Hasegawa's interest in this series. Sounds like a good paranoia series.
[ Spoiler ]
They arrive in silence and darkness. They descend from the skies. They have a hunger for human flesh. They are everywhere. They are parasites, alien creatures who must invade–and take control of–a human host to survive. And once they have infected their victims, they can assume any deadly form they choose: monsters with giant teeth, winged demons, creatures with blades for hands. But most have chosen to conceal their lethal purpose behind ordinary human faces. So no one knows their secret–except an ordinary high school student. Shin is battling for control of his own body against an alien parasite, but can he find a way to warn humanity of the horrors to come? Winner of the 1993 Kodansha Manga Award.
Seizon - Life by Kaiji Kawaguchi
I've not read this, but I've heard tell of it in some circles. Sounds like it could be an interesting small tale.
[ Spoiler ]
Takeda is diagnosed with cancer and feels that he has nothing to live for. His wife also had had cancer, had died of it in fact, and his only daughter has been missing for fourteen years. One day, when he is about to attempt suicide, the phone rings. It’s the police, and they inform him that the dead body of his long lost daughter has been found, that it appears to have been a homicide. Takeda is crushed but resolves then and there to spend the remaining days of his life hunting down his daughter’s killer.
A Spirit of the Sun by Kaiji Kawaguchi
Not read, but it's about politics and national identity from what I gather.
[ Spoiler ]
Japan is hit by a series of monumental natural disasters that leave the country fragmented and its people devastated. Follow the lives of its citizens as they deal with massive emigration to refugee camps on the Asian mainland and try to solve the political task of rebuilding their nation.
Zipang by Kaiji Kawaguchi
Includes a most awesome IJN officer. Lots of ideology and some tactics/strategy.
[ Spoiler ]
A modern Maritime Self-Defense Force vessel gets time-shifted into the Battle of Midway. Follows the crew of the vessel as they struggle to determine whether to stay aloof to the war, or assist their imperialist past. A decent amount of Anime based on this series is currently available in English.
Black & White by Taiyo Matsumoto
This mainly tripped my grit detector.
[ Spoiler ]
Orphaned on the mean streets of Treasure Town, lost boys Black and White must mug, steal and fight to survive. Around them moves a world of corruption and loneliness, small-time crooks and neurotic police officers, and a band of sadistic yakuza who have plans for their once-fair city. Can they rise above their environment? Recently adapted into Anime.
NOiSE by Tsutomu Nihei
I have a bit of a Nihei obsession. I've not yet read NOiSE, but it's related to Blame! so I'd suggest it.
[ Spoiler ]
A police officer in a post-apocalyptic subterranean city investigating the disappearance of a number of children. NOiSE is a one volume prequel to Blame!. It touches on the Megastructure's origins and initial size, as well as the origins of Silicon life. It also includes an early Blame story that debuted in 1995 -this first published piece by Nihei introduces a number of elements that appear in altered forms in his later work.
Blame! by Tsutomu Nihei
You've heard other people reccomend it. An info dump describing it is what I bring to the table.
[ Spoiler ]
Killy is a man of few words. He wanders, seemingly endlessly, through a lonely, gargantuan labyrinth of concrete and steel, fighting off cyborgs and other futuristic nightmares, searching only for something called Net Terminal Genes. And he has a very powerful gun, which he uses without hesitation whenever anything resembling danger rears its ugly head. Who is this quiet, violent, determined man and what are these Genes he seeks? The small communities he finds tucked into the crevices of this towering, distopic ruin hardly give him leads on his treasure, driving him to find larger enclaves of civilization where people can reveal more about the world he lives in and the quarry he seeks.
Blame: Net Sphere Engineer by Tsutomu Nihei
Same Nihei style, same Nihei world. Read a chapter or two, looked interesting and stays away from the heights of raw force that Blame! tended to wallow in.
[ Spoiler ]
The much-awaited sequel to BLAME! follows a man, called a Dismantler, who is in charge of sub-dividing the nexus towers that incur Safeguard interference upon its detection of humans without the net terminal genes. Although humans are once again able to reside in the Net sphere, the Safeguard are still a threat. The Dismantler or NSE, or Net sphere engineer, goes on a journey to aid mankind in their survival.
BioMega by Tsutomu Nihei
If you want to see a talking bear with a rifle, this is the manga for you. Despite the bear, it's got some classic Nihei scenes and his nice high cotrast artwork.
[ Spoiler ]
set in the not-so-distant future (3005 A.D.). BioMega follows a character by the name of Kanoe Zouichi and the mysterious Kanoe Fuyu whose luminous form is integrated into the system of his bike. They are agents sent by a powerful organization to retrieve a human with the ability to resist and transmute the NS5 infection that is spreading across the world.
Helter Skelter by Kyoko Okazaki
I've not read it, but if this manga can deliver on the cheque issued below then it should be well worth reading.
[ Spoiler ]
Through round after round of extensive plastic surgery and vigorous maintenance, Ririko has become the absolute manifestation of beauty, and becomes a wildly successful model, actress and singer. However, soon her body, unable to withstand the burdens of surgery, begins to crumble, and along with it so does her mind, as she plummets towards a frightening and inevitable end.
Monster by Naoki Urusawa
Read quite a few volumes. Can't remember if someone already suggested it, but I'm up to my eyes in a post already, no point in skimping.
[ Spoiler ]
Monster weaves the riveting story of brilliant Dr. Kenzo Tenma, a famous surgeon with a promising career at a leading hospital. Tenma risks his reputation and promising career to save the life of a critically wounded young boy. Unbeknownst to him, this child is destined for a terrible fate. A string of strange and mysterious murders begin to occur soon afterward, ones that professionally benefit Dr. Tenma, and he emerges as the primary suspect. Conspiracies, serial murders, and a scathing depiction of the underbelly of hospital politics are all masterfully woven together in this compelling manga thriller.
Planetes by Makoto Yukimura
Anime adaptation, but this is sure to be glorious in Manga. I've seen the anime only. Hard Scifi.
[ Spoiler ]
Haunted by a space flight accident that claimed the life of his beloved wife, Yuri finds himself six years later as part of a team of debris cleaners on a vessel called the Toy Box charged with clearing space junk from space flight paths. The team consists of Hachimaki, a hot shot debris-man with a sailor's affinity for the orbital ocean; Fee, a chain-smoking tomboy beauty with an abrasive edge; and Pops, a veteran orbital mechanic whose avuncular presence soothes the stress of the job.
And now for things I'd suggest from outside this particular file.
Blade of the Immortal by Hiroaki Samura
Beautiful artwork, characters across a wide range of personality types. Interesting in historical context.
[ Spoiler ]
Manji has killed 100 people and has been cursed to walk the world forever, unkillable by almost all means, by an ancient immortal. He seeks to remove his immortality by killing 1000 "bad" people and, in the course of doing so, is hired by Rin - daughter of a slaughtered sword school - to seek out and kill her father's killers.