Vinland Saga
Historie
Sanctuary
Rainbow
Kiseijuu
Holyland
Ibara no Ou
Shi ga Futari o Wakatsu Made
Gantz
Elfen Lied
Karei naru Shokutaku

In no particular order,

Liar Game, Gantz, Zetman, 20th Century Boys, Chi's Sweet Home (it's published in a seinen magazine), Vagabond, Monster, Ghost in the Shell, Twin Spica, Akira

Who else here reads Zetman?

Manga Therapy - Where Psychology & Manga Meet http://www.mangatherapy.com

1. Kokou no Hito
2. Nononono
3. Vinland Saga
4. Wolf Guy - Ookami no Monshou
5. Vagabond
6. Planetes
7. Chobits
8. Berserk
9. Futari Ecchi
10. Oyasumi Punpun

It's a really tough call about the ratings. I consider numbers #1-7 very much on par/equally good, they're all awesome and made me really enthusiastic reading them. However, for the moment Kokou no Hito takes the lead. So dark, deep and yet fun to read, while delivering awesome graphics and double spreads so frequently.
The others all severely differ in style, but all excel in their genres in my opinion.

I'm a little worried about the latest developements of Nononono though. I don't see a problems with the content and atmosphere for itself (yeah this is pretty hard stuff going on, but some variety does a story good), but I think the staging was not neatly done. Yet I think it will return to usual soon (or already is doing so), a small off-time of so few chapters won't affect the overall image in the end.

Berserk used to belong to the very inner circle of favorites, but the "latest" arcs kind of ruined that for me. For a moment I was thrilled about it once more, when I reread the earlier chapters for recapping Guts' character developement in his dark life - but pretty much at the moment he met Schierke his developement was kind of complete and nothing amazing followed anymore, while the story turned away from the so dark setting. To me it feels too Shonen ever since (Yeah I know this term is kind of missplaced here. But cmon, what's going on ever since, it feels like an OP-alike adventure stuff and doesn't show so much of great characters like Guts and Caska anymore)
Yet, it's not like I'ld drop it out of such a list because of that. It delivered pure awesomeness for so many years, those cannot just be ignored.

This list might change, I still have a lot of great Seinen to read (after all I almost stopped caring for Shonen, I might try out one or two Shojo/Josei though for the sake of a difference). But for the first 7 I'm very sure that they'll always remain part of this list.

Genshiken
Kodomo no Jikan
Black Lagoon
Yotsubato!
Nana to Kaoru
Tekkonkinkreet
Bokurano
D-ASH
Swweeet

I was going to add things like Franken Fran and Hyakko, but those are Shounen? Wow.

1. Yokohama Kaidashi Kikou
2. Ghost In the Shell
3. Blame!
4. Berserk
5. Planetes
6. Sanctuary
7. Twin Spica
8. Gunslinger Girl
9. Blood Alone
10. Ciguatera

--
"They're talking to their balls." (FMP Fumoffu)

I can only recall a couple legit seinen titles that I've read.

Elfen Lied

For me, that's the polar extreme of Seinen that I've had the chance to read so far. I'm sure It's not the darkest, but it's pretty f***ing dark. So much mutilation, so many dead, so little hope, so dark the depths.

http://i1081.photobucket.com/albums/j345/0Fragmaster0/Profiles%20and%20Signatures/FragmasterEdit.jpg

My top ten, can't be bothered to put in order 😛

Berserk
Music of Marie
Blame!
Arakawa Under the Bridge
Brothers of Japan
Freesia
Solanin
Children of the Sea
Piano no Mori
Ultra Heaven

[img]http://i53.tinypic.com/730a6s.png[/img]

Here's my top 10. a bit unusual I guess....

Planetes
Akira
Munou no Hito
Imomushi
Vinland Saga
Ultra Heaven
Ghost in the Shell
Music of Marie
Summit of the Gods

1 - Monster

and after that there are so many really good ones which are impossible to separate. Most of them already mentioned although I would like to highlight Solanin as an astounding slice of life.

Furthermore thanks to the people that mentioned "planetes" as I haven't read that one yet and seeing how similar my tastes are overall with most people in this thread I'm guessing I'm going to enjoy it 🙂

In no particular order:

1. Until Death do us part
2. Jiraishin
3. Kingdom
4. Vinland Saga
5. Chunchu
6. Zetman
7. Threads of time
8. Souten Kouro
9. Sidooh
10. Dance in the Vampire Bund

vagabond
the breaker
yotsubato!
real
maison ikkoku
oyasumi punpun
arakawa under the bridge

Hikari no Machi
Subarashii Sekai
Sekai no Owari to Yoakemae
Nijigahara Holograph
Oyasumi Punpun
Solanin
Bokurano
Narutaru
Bradherley no Basha
Ohikkoshi

Kimi ni Shika Kikoenai
Omoide Emanon
Kizu
Shounenshoujo Ryouryuuki
Vandemieru no Tsubasa
Watashitachi no Shiawase na Jikan
Hotel
Present
Higurashi no Naku Koro ni - Onikakushihen
Shaman King

recently enjoy reading these kind of manga 😀

My top 10:
1.Berserk
2.Lone Wolf and Cub
3.Vagabond
4.Jiraishin
5.Shin Angyo Onshi
6.Shamo
7.Vinland Saga
8.Blade of the Immortal
9.Blame!
10.Threads of Time

Less known manga:

Tropical Citron
Uncivilized Planet
Skyhigh
Freesia
Bokko
Lament of the Lamb
The Music of Marie
Sukima Suki

[img]http://img858.imageshack.us/img858/323/manga.png[/img]

1.HISTORIE
2.full metal archemist
2.oyasumi punpun
3.Otomegatari
4.evangelion
5.route 20
6.Kiichi!!

7.akira

8.March Story
a lot i don't remember
NOT ALL ARE THE BEST BECAUSE I DONT REMEMBER ALOT OF THEM BUT HISTORIE AND PUNPUN ARE EXTREMELY GOOD;HISTORIE IS THE BEST IVE READ IN MY LIFE AND I AM FUCKING 19

Quote from Lilanar

vagabond
the breaker
yotsubato!
real
maison ikkoku
oyasumi punpun
arakawa under the bridge

you have good taste, try historie and otomegatari

Quote from uNpreDicTed

1 - Monster

and after that there are so many really good ones which are impossible to separate. Most of them already mentioned although I would like to highlight Solanin as an astounding slice of life.

Furthermore thanks to the people that mentioned "planetes" as I haven't read that one yet and seeing how similar my tastes are overall with most people in this thread I'm guessing I'm going to enjoy it 🙂

try historie, if you dont put that one on number one then i guess you have different taste

My preferences have changed quite a bit since I first posted, so here goes with my current favourites;

1. Mushishi (This will always be on the top of my lists...unless I change into a completely different person)

After that, in no particular order;

Saikyou Densetsu Kurosawa (The only manga that managed to bring me close to tears -- and several times, at that)
Noramimi
Pluto
Monster
Takemitsu-Zamurai
Ping Pong (I'm surprised I like a sports manga this much, but I do)
20 Seiki Shounen
Tekkonkinkreet
Chii's Sweet Home
Vinland Saga
Historie
Yokohama Kaidashi Kikou
Hanaotoko
Liar Game
One Outs
Billy Bat (Though I'm not sure about this since it's ongoing)
Chinatsu no Uta
Under Execution Under Jailbreak (Very weird, but in a good way)
Majo

I kept it down to 20, but of course there are more. Hardly surprising, since seinen is the demographic in which you can usually find the smartest, most well-thought-out manga.