This forum seems to rely on shounen manga mainly, but once you get to a certain point when reading manga, you'll start to question wether there isnt anything more mature. And I thought we'd use this topic to talk about some awesome seinen!
Personally I'm not that much into violent seinen, when I read something mature I prefer reading something psychological or slice-of life.
Say hello to Black Jack
Probably the one that opened my eyes for seinen, starts off pretty slow but gets very intense after a few volumes. Too bad the scanlations stopped, but for the few lucky ones that know french, dutch or japanese; stick with it and you wont regret it!
About a young man who starts his career as a doctor but quickly finds out about the "dark side" of the medical world.
This manga had such an impact in Japan that they even changed laws!

The artwork is very good too, and that's always a plus! I think you can get the first volume on
www.toriyamaworld.com
Monster, 20th Century Boys & Pluto
By grandmaster Urasawa, probably the best writer in seinen manga ever. Thrillers like you'll never see another in manga. Epic of proportion, dark & twisted underneath, plot-twists up the wazoo. Just stop reading this and go read them instead.
Mangascreener
You might think "Huh, is that even a manga?".
No, it is not. But it is without a doubt the BEST seinen scanlation group there exists. High quality releases of the best you can find in its genre. They did Monster & 20th Century Boys too fyi.
Just check out anything there and you're bound to find something to your liking if you're searching for intelligent manga.
Personal favorites:
Ryuguden, Homunculus, Mushishi, Ciguatera, Vinland Saga
the url:
www.mangascreener.com
Especially
Homunculus is one of the most twisted rides ever. It's by the guy that did the manga of
Ichi the Killer (which the movie was loosely based on, but the manga is so much better and even more insane).
What really caught my attention about this before I started reading it was the story, allow me to quote:
Homunculus tells the story of a middle aged man, who spends his days living in a car, smack inbetween a park infested with homeless people and a large, upper-class hotel complex. He has nothing, yet he is always classily dressed and looks well taken care of, despite the fact he sleeps in his car. Once a day, he always takes the car out for a ride, no matter what the weather. One day, an oddly dressed young man approaches him, and asks him if he would like to participate in a little experiment... Involving having a hole drilled in his skull. He promptly refuses; he has no need for money anyway. The next day, however, his car runs out of gas and gets towed. Desperate for money to get his car back, he approaches the young man and accepts to have the hole drilled in his skull. ''A safe procedure.'', he is assured. But then, of course, that's when the side effects kick in...
The madness really kicks in at volume 2.
Zetman
This is probably the only exception as far as violent manga go in seinen. But I'm just a mad fan of Masakazu Katsura's artwork.
The same reason I loved I''s so much, despite I'm not
that big on ecchi.
It's like a superhero comic, but manga-fied. It starts off slow, but there's enough to hold your attention till the later volumes.
and last, but definitely not least (I'd even say best)
is
Yokohama Kaidashi Kikou
The most relaxing, mind-massaging manga you'll ever read. It's basically about a female robot called Alpha who tends to a little café in a post-apocalyptic Yokohama.
Don't expect any sci-fi action, these are all just slice-of-life stories that totally make you chill out. Very beautifull artwork, especially the environments.
some links:
http://www.cafealpha.org/
http://ykk.misago.org/
http://souhaku.ufpag.com/index.php?m...age&PAGE_id=22