This would be like 75% of my reading list. Well, mainly because I read a lot of series. I also tend to forget a lot of the series I read and I end up just rediscovering them and archive-binging.
Koi Dano Ai Dano: Hands down of the best shoujo I've read, primarily because of theheroine
and the focus on the, err, "politics".
Gamble Fish: One of those mind game/gambling mangas but considerably... quirkier.
Countrouble: Typical shonen romance thing about a guy too shy to confess to school-idol girl and some angel who helps him out in his romantic affairs.
Gordian Knot: Yet another gambling manga, but the lead guy is just doing it for the thrill. And it hasn't been updated in a loooong while.
Shingeki no Kyojin: Post-apocalypse, last humans on Earth trying to survive while gigantic skinless humanoids called the Titans amble around defying the laws of thermodynamics and apparently kill humans just for the hell of it. It's apparently popular, though I don't see much discussion about it.
Btooom: Survival game on an island. Gimmick: the weapons are all various types of bombs.
Iris Zero: Uhhh... check out the page.
Chocolate Cosmos: Uh... it's a shoujo, girl looking for love, blah blah blah. It has nice art.
Ikigami: Japan has this law where someone below 30 is chosen at random to die in order to "remind the Japanese people about the value of life". The manga deals with the guy who has to break the news, and the people who get chosen and of course how it affects not only them but the people around them.
Coppelion: A trio of genetically altered girls wander radioactive Japan in search of survivors and whatnot.
Maoyuu Maou Yuusha: The Hero confronts the Demon Queen but quickly finds out that she's not the ultimate bad guy. The Demon Queen proceeds to teach the hero ECONOMICS to show him exactly why the people are suffering. Think Spice and Wolf
with a big helping of a action/fantasy parody.
Lequios: There is a strange figure floating in the air in Okinawa, that is disintegrating hellfire missiles from US helicopters. Experts from different disciplines and organizations have gathered to figure out what is going on. <— summary from mangareader
Tegami Bachi: Mailmen fight giant bugs with the power of HEART
Paradox Blue: Supernatural beings called Angels test humanity by giving them riddles; those who answer correctly get rewarded, those who don't, well...
Metallica Metalluca: Typical action shonen whose gimmick is that there are a lot of crazy metals with weird effects, and the lead can forge these metals with his bare hands.
Aiyoku no Eustia: Can't be bothered to summarize it... it's some VN adaptation.
And those are all I can think of at the moment.