From RebelliousArt:
Asahi, desperate after the loss of her best friend and boyfriend, came to the abandoned elementary school above the hill. It has been said that it's a cursed place that it will be the last place you will tread in. Those who live will not be able to return. And there, Asahi meets...!?

A series of oneshots.

Sana Kurata, a child actress, faces many problems in her classroom, including a major one - her bullying classmate, Akito Hayama. Sana's outgoing and friendly nature leads her to work towards correcting all of the problems around her. Her 'meddling' irritates Hayama but at the same time captivates him, just as Hayama's gloomy nature irritates Sana and compels her to change him. As these two opposites attract each other, they face many hardships which bring them closer to a mutual understanding.

This manga won the 1998 Kodansha Manga Award for shōjo.

Daisuke is a 23 year-old new schoolteacher. He ends up being put in charge of a 3rd grade elementary school class since the previous teacher quit, and in that class there's a girl who's quite a troublemaker--Rin Kokonoe. You could call her a masegaki (used to describe a kid that acts more like an adult in some ways), and she's also part tsundere (though more dere than tsun).

Peace seemed to have finally found its way into the Obinata household, but through an unexpected turn of events, Shuu and his adopted son, Yuuta, are faced with a disagreement that might change their forever. When their respective lovers, the eldest Obinata brother Taiga and Mayumi, the youngest, are dragged into their conflict, and Yuuta runs away from home, the whole family's living arrangement gets off balance. Will the peaceful days ever return?

Mainichi Seiten series:
Vol 1-2 Mainichi Seiten
Vol 3-4 Kodomo wa Tomaranai
Vol 5 Children's Time
Vol 6-7 Kodomo no Iibun
----Aki-chan no Iibun
Vol 8 Isoganaide
Vol 9-10 Hanaya no Nikai de

From Del Rey:

Najika is a great cook and likes to make meals for the people she loves. But something is missing from her life. When she was a child, she met a boy who touched her heart–and now Najika is determined to find him. The only clue she has is a silver spoon that leads her to the prestigious Seika Academy. At Seika she meets two brothers Daichi and Sora, could one of them be the boy from her childhood?

Won the Kodansha Manga Award for Children's Manga in 2006.

Rinne Ikaruga is just your average 16 year old girl, trying her best to get by. One day, she receives a package addressed from her sister, inside of which is a little girl who just happens to be part planarian and can multiply.
A planarian is a kind of non-parasitic flatworm organism.

Pilot for D. Gray-Man.(http://mangapark.com/search?q=dgray-man)

Fujita is a second year middle school student with a face as pretty as a girl's. On top of that he's whimpy and a bit of a crybaby so he's often confused for a girl. Echo-chan is a fairy who promises to grant his wish and turn him into a strong and attractive man capable of sweeping Onigasaki, his unrequited love, off her feet if he agrees to help her.

From Karma Falls Scanslations:

Because of a frightening experience three years ago, the boy Sata Senda became a compulsive cleanliness freak. As he has anti-bacterial spray and mask as standard equipment and doesn’t allow any form of close contact, he has no friends… Thus came the summer of sixth grade. Sata, who has been half forced to participate in the school trip, arrives to the meeting place completely wrapped in a protective suit?!

From Transcendence:
High school student Asahi is forced to provide blood to a childlike vampire Hikato, and becomes his "temporary" mother, until he reverts to his original self. When Asahi finds out that Hikato stayed behind to protect the human world, how will her thoughts towards him change….!?

A girl granting a little boy's wish...

From Taruby:

Our protagonist, Moji Shimeta, just so happens to fulfill the stereotype for being a worthless human. His inability to carry out a conversation has left him at the bottom of the barrel as far as friends are concerned.
That Shimeta fell in love with the school idol Ishikawa Yuuko, however that kind of love is absolutely, perfectly, and completely impossible. During this time, the messenger of the gods, Osaki, appeared to grant Moji's request with a price attached concerning Moji's cooperation in catching some runaway evil spirits. However to catch them all, Osaki uses Moji as a vessel to become a servent of Uganomitamanokami (aka Inari) called Youko. Lots of Ecchi situations and humiliation abound at Moji's expense.

Ohisama Egao collects the stories of the budding romances of three schoolgirls and one teacher - Aoi, Ryouko, Shizu, and Awada-Sensei - and also shows how their lives intersect at school, a small cafe, and elsewhere. Things don't always go smoothly with the schoolboys they like, but like the sunflowers that surround them, the girls keep looking for the sun.

- polm23

In the Noramimi universe, most families own a 'mascot'. These strange and amusing creatures live at home and act as companions for younger children.

Noramimi is one such mascot. Unfortunately for him, he is an ogre type and thus not popular with children, who prefer 'cuter' alternatives. Unwillingly, he decides to 'home stay' at "Hello Kids" - an agency that organizes matters between mascots and humans.

But, like all mascots, his heartfelt wish is to one day be adopted by a family...

The son of a famous pianist, music student Shinichi Chiaki dreams of studying abroad and becoming a conductor like his mentor. Unfortunately, his fear of flying grounds his lofty plans! As he watches other classmates achieve what he has always wanted, Shinichi wonders if he should quit music altogether.
Then one day he meets fellow student Megumi Noda, also known as Nodame. This oddball girl cannot cook, clean, or even read a music score, but she can play the piano in incomparable Cantabile style. And she teaches Chiaki something that he has forgotten: to enjoy his music, no matter where he is.

Winner of the Kodansha Manga Award for Shoujo in 2004.

This is a story about 2 childhood friends, Masato and Yuki, that reunite as teenagers. Masato is surprised to find that Yuki has become so cute, but even more surprised to realize that Yuki was, and still is, a guy. Yuki's affection for cross-dressing leaves Masato with feelings of discomfort and fright.

On the last day of school, Mihane confesses to her senpai the long-term admiration she's had for her ever since they met, as well as tells her that she will try her best to enter Niji no Oka Girls' Academy next year, the school to which her Senpai is going to attend. Now, one year later, she's managed to pass the entrance exam to the prestigious school and is taking the bus to the school. Unfortunately, she takes the wrong bus, but encounters an interesting first-year girl, like her, that is also set to attend Niji no Oka Academy.

Hilarious!

The Hinomoto Kingdom's Princess Guard is an elite squad that directly protects their royal princess. Kasuga Haru was newly appointed to this prestigious position and was stationed next to the Kingdom's one and only princess.

There's only one problem. Their "royal princess" is a hikikomori, a recluse who stuffs her room with video games and refuses to leave even a nanometer-length out of her room, much less let anyone in. Kasuga's special mission given by the Queen is to make Princess Terras into a proper human. Can Kasuga succeed in turning this otaku princess into a proper princess full of charm and beauty?

Yoshino Nako has a saying. "If I'm happy, I can do anything!"

In her sister's place, Nako-chan steals the groom of an arranged (political) marriage and helps them elope. But when the Hayami group starts failing, she must pay the consequence by housing the delinquent brother...

From Perfect Illusions:

Reo-chan, a first-year girl, gets dumped by her boyfriend because she's not skilled in the home economic traits he believes women should have. Her ex tells her that she must apply to a "housework" club before he will reconsider going out with her. Therefore Reo-chan has little choice but to join.

Here's the catch: the only members are four gorgeous bishies. The other first year in the club, Irinaka, competes with her a lot. As the story progresses Reo and Irinaka get forced into a lot of interesting situations together and in the meantime become closer and closer.