From Eclipse Scans:
A school where the students make their own riches. From Models to Computer Geniuses, These students get rich on their own.
Namu goes to a school where all the elite get idolized by the non-elite. Never making it easy to get to school on time, Namu is soon helped by a new transfer student. Who gets categorized as an elite almost immediately?

Kaguya is a boy in an all-girls' school for demons [fox spirits, succubi, werewolves, etc]. Being the only human is bad enough, but the added risk of his manhood being discovered makes for silly and unbelievable (deliciously enviable) situations.

Yamanobi Apartments have a story behind them: Anyone who lives there will gain something big, but lose something big as well. This is a collection of stories about the various tenants and their love lives.

1) Muroi Kaname has just moved into Yamanobi. The naturally unsocial Kaname doesn't care about stories, and also quickly manages to alienate himself from everyone in the building. But when his upstairs neighbor, talkative Fujimura, sees a different side to him, he's determined to be Kaname's friend. Kaname slowly lets himself grow closer to Fujimura, but will their friendship withstand the jinx?

2) Kamimura Mizuki has always chosen lovers for their looks, and gotten nothing but trouble. This time he wants a sincere guy, and he already has one picked out: Itokawa from his work. But getting his attention is proving to be somewhat difficult. At least slacker apartment caretaker Akabame always listens to his troubles...

3) Nojima is known as the life of the party, always light-hearted and in a good mood. But he's really a bundle of insecurities! He's hiding a secret love for cool classmate Kariya and has moved into Yamanobi for the jinx. But his secret love is slowly turning him into a stalker!

extra) Kanata has been in love with Soejima Ibuki for two years now, but he always sees Soejima-san with a new partner. Will Kanata be able to tell Soejima how he feels or will he suffer with an unrequited love forever?

extra 2) 3 short comedies on the residents of Yamanobi Apartments.

Werewolves, demons, monsters, vampires. All these ferocious creatures are afraid of the same thing: the beautiful Princess Hime, an awesome warrior who fights off the forces of evil with a chainsaw and a smile. Not only does she look great in a tiara, she has power that allows her to raise the dead. She's a girl on a mission, and with the help of her undead servant and a supercute robot, there's no creature of darkness she can't take down!

Always a very tall and stern man, Matsudo has recently joined the student council as the treasurer. To his distress the rest of the members of the student council are nothing but extremely gorgeous and lazy girls... Will he be able to say "no" when they ask him to do their work for them?

High schooler Jenny You is living a dream. In the public eye, she is a delicate princess, a successful pop star, but in real life, she's a rebellious beauty ostracized by her female schoolmates. She and her classmate, Eumpa Won (One), seem to have nothing in common on the surface. Eumpa is a quiet boy, ignorant of the pop culture that has enchanted most of his peers. Having spent his childhood as a depressed prodigy in the United States, he has now resolved to lead a normal life as a regular boy. He likes a cute-but-average-looking girl, Young-ju Chae. Young-ju takes him to a pop concert, and Eumpa is exposed to Jenny's music for the first time. Meanwhile, umpa's resolution to live a normal life is challenged when his music teacher steals the young man's music and attempts to pass it off as his own... So begins the story of One...

The story sets one month after Eita and Masuzu start dating, and sets itself on a "what if" scenario where the Harem element is stronger than in the original.

Otokojuku - a private school for juvenile delinquents that were previously expelled from normal schools. At this school, Japanese chivalry is taught through feudal and military fundamentals. Similar to an action film, the classes are overwhelmed by violence. Only those who survive it become true men.

from Renta!

From Intercross & Shoujo Crusade:

Chika has always seen Murasame-kun as a rival who manages to constantly piss her off. While wondering out loud to herself, her sister whom overhears Chika, gives her a perfume necklace which supposedly able to capture a guy's heart. The next day, Chika bumps into Murasame-kun and spills all the perfume. As she begins to apologize, he suddenly asks her out?!

From Anime Waves:

Meet Shizuki Maku - to say she looks "above average" would be a slight overstatement, but it's especially bad compared to her older twin brothers, the high-school heartthrobs Retsu and Tetsu. She always wondered whether or not she really belonged in her family, but things take a shocking twist when her brothers plant the suggestion that they may not be related after all.

Now she's supposed to pick one of them to be her boyfriend, all the while defending herself from all the other girls at school who want to keep her "brothers" for themselves! Life isn't easy when you're the ugly duckling!

Sonnan Ja Nee Yo received the Shogakukan Manga Award for shoujo manga in 2006.

From Shoujo Crusade:

Miyako's living her life diligently following rules, just as her deceased father wanted her to. But one day Azuma Koutarou sees her play guitar and blackmail her to join his band. How will she face it up?

There's also three extra stories that are unrelated to the main one.

Tatsuhiro moved to Tokyo to attend an art school and start his new life. In his new room, there’s a small hole in the wall. At first he can see nothing through the small hole, but one night, through the peeping hole, he saw a girl. That’s how his new life starts.

For fighting and humour fans Jo Pae, a not really sane boy, in our modern days, he wants to become emperor of Korea... His first step when he enters high school is to become the leader of the strongest school there is. No one expecting it, he actually takes down all of the school's yankees. Jo Pae is now the enemy to kill! All rival schools wants his head whatever the means!

Without doing much research on the school or surrounding areas, Hibino Ryouichiro picks an art school in Hokkaido. Tricked by the school advertisements, he goes to the campus only to find out it is a desolate and cold campus. The only glimmer of happiness for Ryouichiro are the girls on campus. Just hours after meeting Kisaragi Riho, the cute girl on campus, she seduces him only to find himself outside naked after she is done with him. Feeling heartbroken and used, he finds comfort in Aso Tomoe, who lives on the floor below at the dorms. Although it is freezing outside, it is hot underneath the sheets for Ryouichiro.

Rinne, a huge fan of Buddhism, was searching for a "monk-type," a boy as calm, intelligent and diligent as Lord Buddha himself, when she set her sights on a young, handsome monk-in-training, Yuuryou. She soon learns that this kid, out of his robes, is not her dream boy, but a shallow, irresponsible lady killer who goes by Yura. Is Rinne going to give up on her fantasy, or is there more to Yura than meets the eye?

From Shoujo Crusade:

1-3) Lovers in Conflict
Because of her sister who suddenly ran away, Sagiri ends up getting married in her place. Her husband is hard to understand and is a bit of an S. What will happen to their married life?!

4) Wild Rose's Crown

Vampires have evolved and don't rely on human blood anymore. They now co-exist secretly as normal citizens even though they are still feared and discriminated against by the society. So what happens to a female vampire trying to live a normal school life when she meets the most popular boy in school and accidentally nips his neck?

From MangaHelpers:
Before they enter high school, the boys Meguru and Shou are whining about the fact that neither of them has a girlfriend. A strange, large-breasted woman shows up, claiming that she will fix their problem, and kisses Meguru. This odd occurrence is pushed out of the boys' minds when they meet up with Souko, a friend from elementary school, who is going to be in their high school. She's grown up into a pretty young girl, and it seems like the boys might have a shot with her!
That evening, Meguru realizes that the strange kiss may have had more meaning than he thought: he's turned into a girl! He convinces Shou and his mother of his identity, but no one has any idea how to turn him back. Now he's going to have to learn how to be a girl and let go of his hope of dating his cute childhood friend Souko. What will happen to his hopes for a popular high-school life?

During the summer when everything seemed gloomy I met Sensei and he changed my view on things. The only good trait that Azami, the bashful girl has is that she is honest and diligent. The reason why she kissed him and told him not to forget about her was because she wanted to change herself. During the new school term, the two of them meet again. This time it is at school as student and teacher...

From SCX-Scans:
Though it was a bit strange, three people ended up meeting. One, who looks younger than her age and able to see the supernatural. Another who is possessed by a "Yamanko" which refers to "Yama no ko", or a mountain child. She was possessed due to her bloodline and due to the possession, she has superhuman abilities which she can call upon. Finally, an awkward person who enjoys writing poems. Coincidentally, the three are also classmates.