From Fantasyshrine:

High school student, Kaiya Mito is currently going out with Sakaki Yuma, a young enterpriser. Out of frustration, Mito daringly threatens to cheat on the seemly nonchalant Yuma! What's more shocking is that Yuma seems unaffected by the threat and encourages Mito to do it. So during their vacation in Hawaii, a furious Mito decides to carry out his threat. However, even when he's in someone else's arms, all he can think of is Yuma. But what's the reason behind Yuma's stoic attitude? An adventurous love story.

Mazinger Angels chronicles the adventures of four women who pilot giant robots in the Mazinger vein. The concept is a spoof on the late 70's and early 80's popular TV series Charlie's Angels.

Three of the robots, Aphrodite A, Diana A and Minerva X are from the original Mazinger Z series, while Venus A is from the Great Mazinger series. Their pilots are also traditional characters from Go Nagai's universe, Sayaka Yumi and Jun Hono from Mazinger Z and Great Mazinger respectively, and Hikaru Makiba and Maria Fleed from Grendizer.

The style of the manga highlights the sex appeal of both the characters and the mechas, sometimes similarly to the way Aika's female characters are shown. (taken from wikipedia)

The Norse god of mischief Loki has been banished to the human world in the body of a young boy. In order to redeem himself, he sets up a detective agency and dispels the evil residing in people's hearts. He is joined by Mayura, a spiritually clueless high school girl with a passion for mysteries, and eventually, other Norse gods begin appearing around Loki for unknown reasons.

From Project Bite Me! Scanlations:

The creator of Baoh and Jojo's Bizarre Adventure presents a manga about magic and mysteries! You'll meet him at 13:13 pm, on Friday the 13th. He'll do an uncanny intro where he plays a trick on you! And wherever he goes, trouble seems to always follow. Who is this person who creates such incidents? None other than Cool Shock BT!

From CPM:

An alien armada from Jupiter has amassed enough power to destroy all of Earth's defences. Earth's final hope lies in the Space Battleship Nadesico, a ship created using recently discovered extraterrestrial technology.
Can the Nadesico's rag-tag crew overcome their idiosyncrasies and defeat the alien fleet, or will Earth's last hope be lost?

The manga differs greatly from the anime

Marichen finds herself in a different world when she wakes up. The only way to get back home seems to be finding three elements and bring them somehow back to her dream. The three elements are: Peace, Compassion, and Eternity. Her adventure to seek them out begins, or not.

Note:
The plot is very much incomplete, but the author made a note in the end of the book, stating that she is fully aware of it and that she had to end the series due to some issues. She claims that she plans to restart it one day again, but apparently, the author discontinued this series in order to start a new one, Shining. (JanimeS)

[From Viz]:

Ginta Toramizu is a 14-year-old kid who doesn't have a lot going for him: he's near-sighted, doesn't do well in school, sucks at sports, and to top it off--he's short! But Ginta is a dreamer and has had the same dream 102 times, always in the same fantasy world, where he is a hero blessed with all the abilities he lacks in real life.

Then one day a supernatural figure appears at Ginta's school and summons him to a mysterious and exciting new world! In this strange universe filled with magic and wonder, he is strong, tough, agile--and he can see without his glasses! Thus, Ginta begins a mystical quest in search of the magical items known as "ÄRMS," one of which may have the power to send him home. Joining him on this epic journey are his companion Jack and the valuable living, talking, mustachioed iron-ball weapon known as "Babbo," which everyone wants but, it seems, only Ginta can possess!

In a world where demons and humans are at war, there exists a Demon King, whose voice holds a power that destroys all in its way. When an unusual Hero attacks his castle, what's a Demon King to do other than confess his love? But thanks to meddling minions and the inconvenience of a voice that destroys everything in its path, his confession may not go according to plan...

Abe Maria, an ordinary high-school boy and Nanami Tokuko's childhood friend, is the world's last pureblood vampire!! For 10 years, Tokuko has been encouraging him to become a part of human society, and since then, Maria has come to love humans. As such, Tokuko happily watches over Maria. This couple's story is the world's most gentle vampire comedy.

*Includes an extra story called Manshinsoui no Futari (The Wounds that Cover Us) in vol. 1 detailing a high-school romance between a boy who is suffering mentally and an extremely clumsy girl.

From Mangascreener:

Nawoki Karasawa is one of the longer-active and more prestigious names in the typically small time, lesser-known world of gag manga. In a genre where art skill is second to just about everything else, Karasawa's dialogue is hilariously sharp and witty.

A gag parody of Shinji Nagashima's immortal "Mangaka Zankoku Monogatari" (Karasawa's title only differs by adding "Chou" (super) to "Zankoku"), a manga about the dreams, ambitions, and suffering of a group of bright young mangaka. Karasawa brilliantly takes the piss out of just about everything involved with being a mangaka. It's lewd, raunchy, endlessly cynical and laugh-out-loud funny.

Originally published in Ikki and the Big Comic Spirits special issue "Casual" from 2000 to 2003, it was collected into a single book in 2005.

Tezuka teaches about biology in short installments.

From Del Rey:
Junior high schooler Nina is ready to fall in love. She's looking for a boy who's cute and sweet and strong enough to support her when the chips are down. But what happens when Nina's dream comes true…twice? One day, two cute boys literally fall from the sky: they're both wizards and they've come to the Human World to take the Magic Exam. Their success on this test depends on protecting Nina from evil, so now Nina has a pair of cute magical boys chasing her everywhere she goes! One of these wizards just might be the boy of her dreams…but which one?

From Aku-Tenshi :

Because her father was sent to London to work, Natsumi, a 4th grade student, also must leave Japan along with him. Her classmates throw a farewell party for her. Natsumi is prepared to go to London, but on the night before Natsumi's arranged departure, a baby suddenly appears in her house after a roar of thunder! What's more is that this little baby is actually the one that Natsumi will give birth to in fifteen years!

Mini Drama: Toast
This is a story of a boy who dreams of being with a girlfriend on the night of the first snowfall of the year and a girl who happened to cross paths with on the night of the first snowfall of the year. The girl, however, mistakes him for a pickpocket when he tries to return the wallet that she dropped. Already in a bad mood from a breakup, the girl mysteriously gives him a piece of toast and leaves him standing there in awe. Was it fate or coincidence that those two happened to meet each other on the night of the first snowfall of the year?

It's about a girl, Taobei, who has somebody writing on her book that she's a pig. This really angers her. Then, there's Muyu, the guy who's been friends with her since childhood... and he's angry with her. A really funny story of a silly and dense girl.

From Clamp no Lumiere: Murikuri is the story of a popular pig, a pervert santa claus and his high school girlfriend, nice aliens and many more... It does not make sense and I would advise you to not try to understand it. Murikuri is to CLAMP what special halloween is to the Simpsons, a collection of short gags.

1) Lovers on a Desert/Peaceful Island
The little rich boy, Hiroshigu, went on board a fishing boat out of curiosity as well as for the fun of it. However, he was swept off by waves and ended up on a deserted island with the bodyguard he hated most - Miyakawa!

2) Lift
Akasaka is on his way to a very important meeting when the elevator gets stuck! But he's not alone: Ozawa is stuck with him, and he seems to know Akasaka...

3) Love on a Storm Mountain
Rickshaw driver Hayate was educated about the town by the beautiful Kei, who he first saw dressed as a woman! But Kei is keeping a secret from Hayate...

4) The Gaze That Never Wilts
Itou-sensei just recently transferred to the all girl's school, only to have fellow teacher Tanaka confess to him in public! Tanaka is determined to win Itou over, but Itou just wants to live a quiet life, especially after what happened six years ago at the boys school he used to work at.

5) The Return of the Desert Island
3 page short about Hiroshigu and Miyakawa.

6) Housekeeper Tomioka's Diary
4 page short about Hiroshigu's housekeeper following him to Miyakawa's place.

The story of Nanao Shirahane and Kuon Aikawa from Mujihi na Otoko continues. List of Warui Series: Vol 1 Warui Koto Shitai [1-1] Vol 2 Waruiko Demo Ii? [1-2] Vol 3 Kirai ja nai Kedo [2-1] Vol 4 Koi Ja nai Kedo [2-2] --- Warui Koto Bakkashite GomenNasai [1-3 &/ 2-3] Vol 5 Warui Yatsu Demo Ii [1-4] Vol 6 Mujihi na Otoko [3-1] Vol 7 Warui Koibito ja Dame? [1-5] Vol 8 Kare ja nai kedo [2-4] Vol 9 Mujihi na Anata [3-2] Vol 10 Sunao ja nai kedo [2-5]

From Tokyopop:
Yayoi, a spunky high school girl, has inherited spiritual powers from her mother, and she uses these powers to protect people. During a fight with the devil Ura, Yayoi's power turns the devil into a black kitten. Now, even though Ura doesn't hide his desire to "eat" Yayoi's power when he gets the chance, they develop an interesting relationship: the two begin living together, and Yayoi takes her new feline "friend" on her adventures.

Clay, a child prodigy, was hired at the age of 14 to become a professor to make chimeras, creatures made with a fusion of various materials. However, after he was hired, he was unable to meet the expectations of the company that hired him and was fired. He comes upon an abandoned research facility and creates a human child chimera and names him Muddy. Together, they will go out into the world and find out what Muddy is capable of.