From ADV:
Ahiru wishes to become a beautiful ballerina, but her two left feet always get in the way of her dreams. All of that changes when she is given a magical pendant and is suddenly transformed into Princess Tutu, a graceful dancer who is lighter than air. But not all is well for the crowned princess of pirouettes. The boy of her dreams has a broken heart, and Tutu must collect the shattered pieces to make her beloved Mytho whole again, before a darker dancer takes his heart away forever.

From Citrus Ego:
Marino ran away from home, for her aunt tried to make her marry a strange man. She had lost her parent eleven years before. As she left home uncertain where to go, she traced back in memory, and she arrived at a men's dormitory.

From Manhua-Revolution:
Marino, a 15 year old girl runs away from home due to an arranged marriage, finds her self in a male dormitory by accident, there she meets...

A young lady of the prime minister family, enduring for 8 years. Finally, at one day she was bestowed empress, Phoenix of the country! But life is unpredictable. Her husband loved her stepsister, deposed her as Empress and even forced her son into death. In that Cold Palace, she was forced to drink poisonous wine. So in the next lifetime, she made a promise to never do good deeds and help others, to never step into the palace and to never become the Empress!

Abused like a slave by everyone at school, and battered by the single mother she lives with at home… That was the girl’s, Endou Himeno’s, everyday life. However one day, a ‘wasp’ that stung the girl, changed her fate. Her fate, and that of humanity… Piercing the ‘seed’ known as humanity, a thrilling insect suspense story begins!

Yes it is.

Raws: http://seiga.nicovideo.jp/comic/43318

From Stiletto Heels:
Somewhere along the way, life for high school teen Shima seemed to take a wrong turn. A fall-out with a friend in her all-girl’s school became fodder for nasty rumors, etching her name onto the school’s blacklist. Things at home aren’t looking any better. Her mother seems to be in love with the idea of being in love, and has a string of husbands to prove it. Shima has been silently putting up with her mother’s latest arm-candy, but with her friendships going down the drain, the pressure to escape and start anew has her craving for the bears and Yezo sika deers of her biological father’s hometown in Sapporo.

Priscilla Motia works as a sorceress at the mercenary corps, but she was once the only daughter of a count. Until her father died, and her stepmother made a fortune from selling their valuables to her divorced husband who was 10 years older...

In an accident while working as a mercenary, Priscilla got her hands on the Dragon Heart just before she dies... This is a chance to take back the 15 years that she lost! She is determined to go on a big adventure.

“You're back!"

But what awaited Priscilla was a huge debt caused by her evil divorced husband.

Seeking for revenge, Priscilla goes looking for Kian Rustin, the Black Death of the Battlefield for help and asks, “I have a favor to ask of you."

“What do you want me to do? Is this an assassination attempt?"

"Kian Rustin! Please be my husband."

So, will Priscilla be able to win both land and love?

Riding high on the memory of a boy named Hikaru with whom she spent a day during her last year of grade school, Megu went through middle school without romance. Now that she's a high school student, she has decided she is finally completely over her first love and can look towards the future. But! Megu meets a pretty girl on her first day of high school who gives her a big hug, and her name is Hikaru?!

Note: this manga is currently on hiatus due to its author's copyright infringement. There has been no notice since June 2012 about its re-appearance.

Because of a past heartbreaking experience, Yuki closed off her heart. Not until her classmates dragged her and forced her to attend a group date with the guys from other school. There she met a crybaby Tsuyoshi. The next day, the next thing she knows is that she is being chased by Tsuyoshi saying that he wants her to listen to his depressing love story! But surrounded by the younger crybaby Tsuyoshi and hot classmate Keito, she can't remain uninvolved with love!

A collection of oneshots by Asatsuki Mai.

1. Prism Heart
2. Teen's Road
3. Hot White Kiss
4. 17 Year Old

[From AT-Translations]:

Based on an ero-game, Prism Palette is Peach-Pit’s (famous for DearS, Zombie Loan, Rozen Maiden and assorted other manga) first publication. It follows the main character, Masaki Shirai, as he spends his days at school, surrounded by beautiful girls.

From Attractive Fascinante:

Oomura Yuu's first kiss was stolen by the beautiful Student Council president, Takamura Mitsuya. He later became his executive secretary and his duty was to do whatever Takamura wanted. Both loved cats and were slowly drawn towards each other. As much as Yuu wanted to acknowledge his own feelings, he realised that he might not really knew about Takamura at all. In the end, Yuu decided to follow his heart and reach out to Takamura.

Info from here (and there's lot more info about the two volumes there):

This is a collection of manga short stories done by Takeuchi Naoko, from her debut in 1986 through her first work after the completion of Sailor Moon in 1997.

V.1
• Gradation 1: Tamaki - Peppermint
• Gradation 2: Saura - Sunset
• Gradation 3: Mizuki - Moonglow
• Gomen ne Wednesday (Sorry Wednesday)
• Liner Notes

V.2
• Rain Kiss
• Yumemiru Rainy Button
• Secret na Kataomoi
• Love Call
• Yume ja nai no ne

The demonic overlord has been revived, and kidnapped the beautiful Princess Sina. An army of the world's finest knights has been sent to his castle to rescue her, but Sina refuses to be a mere damsel in distress and decides to break free on her own.

Not to be confused with the manga, Prisoner (Kaen). [From Fushichou]: After Kei Oosawa's father died in an car accident, all he had left was his father's dear friend, Kazuma Takashina. Kazuma, who was still young, took Kei in and gave him a new home. During the years that passed by, a relation of desperation and hate grew out between Kei and Kazuma and the older Kei became, the more he wanted to escape from his 'prison'. Will Kei be able to live on his own, to escape from Kazuma...?

A fateful meeting at the library embarasses Atsurou as he awakens with a man's coat covering him while he was asleep. Disgusted by the smell of perfume, he returns the jacket to the famous translator Taki and quickly makes his leave. But that isn't the last time Atsurou will encounter Taki. When they meet again by coincidence, and Atsurou requests to stay for a night at his home, he finds that Taki isn't as bad as he originally thought...

The day started as any other day for the three sisters, Tsumugi, Momo, and Rin, and their father. But they soon learn that everyone has disappeared and they appear to be the only humans left on earth. How will they survive?

A oneshot about a love relationship between a senior with a junior....

From Shi-ran:

Kasumi's day just keeps getting worse and worse. First he's dumped by a classmate, and then a strange fortune-teller shakes his world as he reveals himself to be in search of a master. And who could the lucky boy be...?

From Aerandria Scans:

His highness the prince of Estolia Wilfred became an exchange student in Eito University. His noble appearance and gentleman’s manners quickly filled the campus with hysterical women’s voices. Miyako also studies at that university and for her master’s thesis, she is determined to interview the prince about his great-grandmother. But when she approaches him about it, she suddenly discovers “the dark side” of his character...?!

Contains Oneshot: Sinful Love ~ Your Future is Mine
Sequel of A Sin to Love You and A Sin to Love You~Can't Live witout You~ from Fu Junai