From DrCoke at MangaHelpers:

When Kamiyama Keito saw Oomiya Honden High School's (a.k.a. "Denkou") Rock Band "Kei-On" club, he was immediately struck by a sense of awe and admiration. Once he was admitted into the school, he immediately joined the club. To the despair of Keito, the club was run by two degenerate senior students who forbid any real practices. Once spring break turns around, Keito finds out that the two seniors were arrested for possession of marijuana, in turn pushing the club into the brink of termination. With the help of the only other member of the club, Tsukumo Shintaro, will Keito be able to prevent the termination of his club?

From Attractive Fascinante:

1-3) Kyoushi and Kou have been lovers for 3 years, and their relationship has been discovered and accepted by Kyoushi's older sister. Now can their love withstand an overbearing, intrusive fan girl? How about an adorable 5-year old cousin who wants to marry Kyoushi?

4) Don't Touch Me
Bittersweet one-shot about the possibility of living life again and finding a new love after being raped.

5-6) Sou and Keigo have been friends for years, but Keigo never realized Sou's secret - his parents are both men. Now that Keigo is beginning to be more concerned about Sou, is it time to meet the parents? Even if both parents are men, will they approve of their son's preferences?

With a deep gaze, Oshima received a confession of "I love you!!" from his classmate, Hiyama.

And naturally, astounded by his confession, Oshima rejected him as he didn’t believe love between men and that made Hiyama became discouraged.

Trying to face with an earnest feeling, he’s immediately became interested in Hiyama. However, Oshima can’t be honest with himself… Are they friends? Or lovers? Be that as it may, both of their relationship will change!!

Lisa moves to Tokyo for university, and she finds herself living with some strange people! The Russian girl Irina explains that the inhabitants work on a time machine together. The other people include Kitsune (who wears a fox mask), Hime (who cooks), and Aki (a self-declared scientific high school genius). This 4-koma style manga follows Lisa's bizarre new life.

From ShoujoMagic:

1) Teach Me More
On her way home from school, Hina is attacked by a pervert on the train! She's too embarrassed to raise her voice, but - she's saved by Kyousuke!? Kyousuke is the hottest guy around, and there's not a single girl who doesn't want him. He pulls Hina off the train, and then... he does more things to Hina than the pervert on the train would have!
(Also included in Yuuwaku - Sakaraenai Yokubou)

2) A Boy's Suggestion
Kana is on a mission of love. How pathetic would it be if a senior like her completed high school without ever having had a boyfriend? That's when Takuya, a freshman with a reputation as someone you don't want to mess with, confidently asks Kana to go out with him. She has misgivings about him being younger than herself, but can she be adult enough to overlook it?
(Also included in 17-sai Hajimete no H)

3) Lewd Melody, Obscene Fingers
Yurika has grown so used to doing what others tell her to do that she never realized she was like a caged bird. She accepted it as a matter of course when arrangements were made for her to get engaged to Satoshi, her controlling piano teacher. That is until piano genius and fringe element Hibiki teaches Yurika how to put emotion in her music -- how to fly from her cage -- among other less innocent things...
(Also included in Love & Sex)

4) Teach Me More & More - How the Wolf Feels
Continuation of Teach Me More. Hina and Kyousuke finally go on their first real date, and we learn how the wolf feels about his rabbit...

5) Haou Airen Side Story - A Tale of Happier Times
Kurumi's brief dream of happier times with Hakuron.

Average high-school student Takahashi wants good luck for the new year so she can get closer to her popular classmate Yoshizawa, but instead her fortune reads "Terrible Luck". What's a poor unlucky girl like her to do?

Chiisaku Furikabutte, lit. “Small Windup”, was published in Afternoon between the tankobon publications of volumes 15 and 16 and during the 2011 hiatus, and it is a series of specials about the lives of Oofuri characters. (Nice Pitching!)

Popular boy Kagami is horrified when his secret is sniffed out by the infamous anime club President, Tsukishima. Tsukishima agrees to keep his secret, as long as he submits to her terms...

Student Council Vice President Harunobu has never fallen in love before. She's dated various people and after recently breaking up with someone, again she finds herself being asked out. Will this girl finally be able to make her feel the heat of love?

A girl gets impatient when she and her boyfriend haven't kissed yet, even though they've been dating for awhile, so she tries to take matters into her own hands.

Also, there's a oneshot after this about a girl with a similar problem as in the first story with her dating the most popular guy at school who hasn't made any moves on her.

Compiled into Kimi to.

Yasoinaba’s very own Investigation Team are back in action in a new adventure based on the critically acclaimed Persona Q series! While enjoying Yasogami High’s cultural festival, the Team suddenly hears the ringing of a mysterious bell and a bizarre, new exhibit appears at the festival. Inside this exhibit is a most curious maze—one that will take them on a wondrous and treacherous journey. And as they explore this labyrinth, they’ll meet new foes and maybe even some new allies from the Persona universe…

Rin was a certified yankee on her first day of High School when her brother dyed her hair blonde as a prank. On her way home, her hair got stuck on the bracelet of famous hair stylist Hanae!
With no way to free her hair from the bracelet, she ended up cutting her hair off!
Hanae said he’d take responsibility for damaging her hair... but what does that responsibility have to do with marriage?!

In the future, an energy source called "Life" has become incredibly important. Certain people are able to synchronize with devices called "Sai" which gives them the ability to extract "Life" and have super powers. These people are known as "Sai Takers." Within the "Sai Takers" there is an even smaller group, "Original Takers." "Original Takers" have a contract with a magical device, and they can manipulate "Life" without the use of a "Sai." These powerful people are also immortal, and they only die if they run out of "Life." The world admires "Sai Takers," but "Original Takers" are careful to keep their identities secret.

Nanase Kyouya is an ordinary teenage boy, who moved in with the girls Igarashi Kyouka and Yuma after the death of his parents. Yuma is a "Sai Taker," but Kyouka is an "Original Taker." One day, he goes with them to see a new model under testing of a magical device, based after Kyouka's. After a deadly terrorist attack, Kyouka desperately contracts Kyouya to the new device model to save his life. The device has some side effects, however, one of which is that it transforms Kyouya into a girl! Now Kyouya is secretly an "Original Taker", and he must go to the elite "Sai Taker" school, as a girl, with Yuma. Will he be able to keep enough "Life" to stay alive? Will he be able to navigate his life as a girl? What other side effects of this device lie in wait for him?

These people have been living unhappy lives because they've never been able to do what they want.

Ga Yeon's smart, but wants to become a singer. However, the Korean educational system strongly enforces studying to students without considering the goals and dreams of the student. She's been forced to live a life of suppression.

Jae Hee is a piano player, but he's been living in constant delusion of his life. He has mental problems and cannot distinguish reality from a dream.

Dong Woo and Min Seo are a couple who are talented musicians but cannot make music they wish to make because of the current situation of the Korean music industry.

Hyuk's a very good guitar player, but is forced to be in an idol band, rather than what he really wants to be. The 5 come together to make a band of their own.

Hoshi is just your average student until one day, he encounters an oddball upperclassman stuck inside a locker.

Eren and Mikasa enter a new school-- Titan Junior High! However, Eren's hated Titans for years-- can he get along with his new (harmless?) classmates? Featuring all of the characters from the main series as you've never seen them before, this series is sure to delight fans of Attack on Titan with a human vs. Titan volleyball match, a Titan rock band, and much more!

Come spring, Nishiwaki Haruka becomes a second year high school student. For a second time. Due to accidents and illnesses, she didn't have enough attendance, thus the repeat year. She transferred to Yamabuki High to run away from her old friends. One day, the baseball team from her old high school came for a friendly match, and Haruka bumped into some old friends. Her new classmate, Ono Kenta, found out her secret. She agreed to be the manager-cum-player to their weakling baseball team in order to keep him from telling her secret...

The second shounen-ai manga ever published, The November Gymnasium focuses on chaste, yearning love between boys at a prestigious German boys' school.

Contains Poor Mama (Kawaisou na Mama)

Ayase Michiya is a playboy who always has a new girl on hand, but the one whose attention he craves the most is unexpectedly his best friend, Satori Kouta. Trying to stay cool about it, he sets up Kouta with a girl, but things don’t go as expected...