Here are some of the previously suggested ones that I've already read.
Biomeat - I love it.
Psychometrer Eiji -
Spoiler (highlight to view)
seriously? Only a kiss on the cheek at the end?
Remote - Nice ending.
B. shock! -Excellent choice, even if its a bit dated. This was more a romantic comedy, though.
Hoshi no Samidare -One of my all time favorites. It Charmed me.
Kurozuka -It's not really that happy of an ending, when you think about it.
Psycho Staff -So much lost potential here---it's far too short.
Sukimasuki -I had fun with it, but again, it's a short and sweet tale.
Hanako to Guuwa no Tera -I loved this one. Very much. But it seemed a bit rushed at the end.
Mahoraba -It's too harem-ish for me, and I sorta don't like the whole split-personality thing.
Mirai Nikki -Great Yandere moments. And nice ending.
psyren -I LOVE this series. So much. It's a straight shounen, though. but wow.
love roma (comedy) -It's wacky and striaghtforward. a bit Shoujo, though.
sanctuary - Excellent series. I've read all of the works of this author. And this and Crying Freeman are the best.
fullmetal alchemist- best mainstream shounen. Bar none. In my opinion, it's one of the all time greats.
Itoshi no Kana - was ok. But to slice-of-lifish, maybe?
Bitter Virgin - Left me happy and bitter at the same time.
Full Contact - It's cool. But I remember that I felt it was a bit too short or shounen-ish (I prefer KENJI)
Open Sesame - I like this series. 'Nuff said.
onani master kurosawa - Masterpiece.
little house with an orange roof - Excellent old-school seinen.
yume de aetara - same as above.
captain tsubasa (they get married...and she's pregnant) -TOO LONG!!!! TL/DR
major ( married ) - TOO LONG!
Parasyte - Read it when I was kid.
Suzuka - It's okay. A bit underwhelming.
Happy World - I've set it aside for reading later
Monster - Same as Happy World.
Emma - It made me rage at its subtlety.
ALL OF ADACHI's STUFF. Especially Touch, Katsu, Rough and Cross Game
Junk - A bit too dark? Maybe if I'm desperate.
Zetman - It's like Junk.
Battle Royale - I liked the movie better.
Planetes - I honestly liked the anime better.
Miman Renai - Cute.
Outlanders - Old. But good, I guess.
Well, that's all I can remember for now. In the hope of facilitating suggestions, I'm adding as an addendum my original post a few weeks ago.
"I've read too many manga to really list (to give you an idea, if I try a search on any category/genre except for Shounen Ai, Shoujo Ai, Yuri, Yaoi and genderbender, I've probably read every single manga of the first page and maybe half of the second page of the search results).
I'm looking for a seinen or mature shounen (like Biomeat, I guess) that ends with the main couple happily together. So far, off the top of my head, the only seinen I can really name is Eden:It's an Endless World (and even in this manga, the lead and copy lady sort of take a backseat to the proto-male-lead by the end of the story, so you only see their happy couplehood peripherally). Psychometrer Eiji and Remote are examples of semi-mature shounens, but both (as the author is wont to do) end with the leads only hinting at a possible relationship in the future, and no real resolution.
Having strong male and female leads is a definite PLUS! I'm kinda tired of the typical weak dork lead used in most shounen (especially HAREMs), and shoujo and josei is riddled with so many pathetic females that I'm sure I'm getting an unbalanced and skewed view of of the Japanese Female Population.
I'm especially in need of a good fix right now, since I just finished reading Hour of Mice (Hatsukanezumi no Jikan) and although it's a great seinen, the love-polygons that concluded with a bittersweet parting between the leads just made me feel like I've been screwed over.
Any suggestions? "
