Here's a few recommendations no particular order and with brief summaries of each (although I also second denpa kyoushi, Mx0 and the world god only knows):
1. Abnormal-kei Joshi: High schooler Shiina Shinya thinks that all girls are pretty much good-for-nothing, mostly because he doesn't understand them at all. That doesn't stop him from being surrounded by strange girls! Tsubasa Tooka, a cute, much-admired girl, stalks him. Shikimura Masami is majorly into masochism, and has recruited Shinya into her play sessions. Ikari Satsuki seems suspiciously interested in the recent serial stabbings, and seems to want to drag Shinya into it. Banjou Yoruko, a normally quiet, bookish girl, has decided she and Shinya are bound up in some fantasy setting. Uchida Yumeji is the school's sleeping beauty, who spends all of her time in the infirmary because she requires so much sleep. Shinya brings her newspapers, so she can keep up with current events in the short time she spends awake. Lastly, Okui Akane is convinced she is a vampire. For all Shinya knows, it could be true, but in practice it just means that he has to let her drink his blood. How will Shinya deal with all these good-for-nothing girls that complicate his life?
2. Shinigami-sama to 4-nin no Kanojo: Minaguchi Kaoru is nothing special. He's no good at sports or school, isn't in any clubs, and he's not popular. He has no friends and isn't even interested in any of the girls he knows. He's also teased due to the fact that he loves shoujo manga. Unlike the harem daydreams of his peers, he dreams of finding his true love. Unfortunately, a shinigami comes to kill him, simply because he's a "forever alone" sort of guy. When he gasps out his intention of embracing life with his final breaths, though, she takes it back! As long as he follows through on his intentions, he won't be killed. To convince the shinigami that his plans are genuine, he declares that he will confess to the girl he likes, the very next day. Expecting failure with confessing to random girls in his school, he sends out love letters to four different girls. To his surprise, they all agree to be his girlfriend. Now, this shoujo-manga-loving guy has ended up in a kind of harem story, quadruple-timing four girls! Will he be able to stay involved enough with society to avoid an early death?
3. To Aru Kagaku no Railgun: Welcome to a world where mysticism and science collide, and supernatural powers are derived from either science or religion. At the heart of this world is Academy City, an advanced metropolis whose population is comprised mostly of students The majority of students are enrolled in the city's "Power Curriculum Program," where they must learn to master their latent psychic powers. Out of several million students, only seven are deemed powerful enough to have Level 5 status. Meet Mikoto Misaka, the third most powerful Level 5 esper in Academy City.
4. 12Beast: From the creator of Monster Musume (really ecchi monster girls) comes a new series, 12 Beast! Join ninja apprentice Eita Touga as he embarks on an epic adventure searching for his missing brother Kouki and save the Autana (Humanoid Beast) race of "Live-Earth" form the mysterious Gigas seeking to exterminate them.
5. Bright World Project: The minister's aide has an idea, a project in mind to help correct the declining birth rates in Japan. This plan, so to speak, has it where Japan's youth are encouraged to form relationships. The catch is that at the chosen highschool for the initial test of this is being held, the project is mandatory — the students must become intimate couples with the other students or they will die.
6. Clockwork (only 4 chapters so far probably dropped as a series but I can hope): Historical gunfights in the meiji era. Story revolves around Katsu Cloak who traveled with his father to America to learn the ideal of "Freedom". Unfortunately, he loses his father and plans to return back to Japan.
7. Hammer Session: Two prisoners managed to escape after the police truck carrying them crashed on the highway. One of them , Mr Sawazaki is a gangster who has sent 10 opposite bosses to hospital. The other called "You" - our protagonist - is a con artist whose cheating profile has piled up to approximately 100 billion yen. Accidentally, "You" then becomes the new teacher for the nearby high school, under the new name Takeda Shindo, and according to a deal of "Hammer Session" with the headmaster. The story is about a teacher who has a past record as a con-artist. It has its own unique taste, which makes it distinctive from other series about teachers, such as GTO and Gokusen.
8. hitsugime no chaika: Toru Acura, an incredibly lazy man with some hidden talents, has been forced by his sister Akari to actually go outside and search for work. However, he is in for a big surprise when he meets Chaika Trabant in the forest, and they are suddenly attacked by a monster! How will they survive? Who is this mysterious girl, and why is she being targeted?
9. Kanojo no Kagi wo Akeru Houhou (stronger ecchi): Haruma's first impression of the new transfer student, Chitose, would be striped panties. Running into her in the hallway, Chitose's panties greet Haruma before they even know each other. Immediately, Haruma finds himself attracted to this mysterious panty girl, only to find out that she is transfering into his class AND she's going to be the new house keeper at his apartment. Let the skirt flying romance comedy begin.
10. Kimiiro Focus: Photography is the art to grasp beauty with the one and only tool, a camera. Oji's dream is to become a photographer that photographs at the front lines of war, to take pictures of historical events taking place in front of his eyes. However, his childhood friend, Sumire, doesn't think that he is capable of becoming one. In his photography club, Oji shows his photos to the group, and his upperclassman, Ran, points out that Sumire is a good target to photograph. Oji manages to get permission to take photos of Sumire, and during his shoot, Sumire notices that Oji is acting differently than before. Later they find out that one of Oji's pictures won an award! Sumire congratulates him, but Oji sees beyond his award. He claims that he learned that he has much more potential than he thinks. Ran, overseeing this, plans to take Oji to the next level so he can capture true beauty through the lens of a camera!
11. LasBoss x Hero: Sagara Masamune is a manga author who isn't very successful, and it's looking like it's time to end his battle manga. To go for an unexpected ending, he plans to kill off the main heroine, Nina, in a dramatic way. As he works on his manga, he is mysteriously sucked into the pages. Now he's trapped in the world of his own creation, with his protagonists, exorcists Haru and Nina. He doesn't really get what's happening, but he thinks concluding the manga, which involves orchestrating Nina's death, might get him back home.
12. Maga Tsuki: One day, Yasuke was working up the courage to confess his feelings for his childhood friend Akari. It was the perfect opportunity, since the two of them were going to eat dinner alone together at his family's shrine. Before dinner, he rushes through the daily shrine rituals and accidentally breaks a sacred mirror. A goddess, who looks like a cute girl, curses him for it, and now he will die if he's ever separated from her. All too late, he learns that she's a goddess of misfortune, and horrible things happen around her whenever she's upset. Will he be able to get the goddess to lift the curse? And how will he ever explain this to Akari?
13. Necro;Cronicle: First two chapters are pretty damn ecchi but the latest translated chapter is actually pretty badass. Kaju is a normal boy, he even has a girlfriend. But his life changes when he is reanimated by a necromancer who wants to conquer Japan. Whatever will happen next....
14. Nozomi x Kimio: Suga Kimio finds himself hiding in the girls locker room, unable to move or escape the situation as the girls in his school crowd in. Although he originally had no ulterior motives, he found himself panicking as he heard the girls coming in and hid in a locker. Komine Nozomi, one of the shy girls in his class finds him, but surprisingly covers for him. Perplexed but glad, Kimio goes home. Later that night, he gets a text from Nozomi who happens to live across the way on the same floor of the complex they both live in. She blackmails him into agreeing to show each other’s bodies when she texts him. Kimio has to abide by Nozomi’s insane demands or risk ruining his school life so they both start their little peep show through each other’s windows…
15. Ore to Hero to Mahou Shoujo: About a guy who reluctantly transforms into a magical girl to fight monsters.
16. shokugeki no soma: Yukihira Souma's dream is to become a full-time chef in his father's restaurant and surpass his father's culinary skill. But just as Yukihira graduates from middle schools his father, Yukihira Jouichirou, closes down the restaurant to cook in Europe. Although downtrodden, Souma's fighting spirit is rekindled by a challenge from Jouichirou which is to survive in an elite culinary school where only 10% of the students graduate. Can Souma survive?
17. Teizokurei daydream: This story is centered on a main character named Saiki Misaki who has two jobs, neither of which she is particularly happy with. Officially she is a dominatrix in a BDSM club who writes a column for a sex magazine. Additionally she works for a government agency, The Livelihood Preservation Group, as a necromancer. The term necromancer in this story refers to a person who can speak to and see ghosts, and who sometimes can allow the ghosts to speak with their voice to people who cannot see the ghost. Her government job usually entails helping to remove a troublesome ghost. This is known as exorcising. Misaki considers her government job to be less respectable than her work in the sex industry.
18. Sorcerer Hunters: In an age of magic and sorcery, the world is divided between those who have supernatural powers and those who don't. Fighting for justice and against black magic and evildoers everywhere are the Sorcerer Hunters: Gateau, Carrot, Chocolat, Mocha, and the rest of the gang. Their quest is to destroy each of the Platina stones- the objects the evil sorcerers use for creating their black magic - in an entertaining mix of farce and adventure.
Just a few not all of them may meet your criteria but you might be able to find something in this list that you might like.
