From Yen Press:
At the invitation of an old school friend, introverted high-school student Mikado Ryuugamine, yearning for a life less ordinary, makes his way to Tokyo. His destination: Ikebukuro, a hotbed of madmen living most unusual lives. On his first day there, Mikado encounters a cast of characters so colorful, the rich hues of his rural hometown pale in comparison! And as if the naive stalker chick, the high school senior obsessed with the rather creepy object of his affections, the hikikomori genius doctor, the hedonistic information dealer, the strongest man in all of Ikebukuro weren’t enough…Mikado also chances upon a sight that leaves him rubbing his eyes and scratching his head — the Black Biker, who is black as night from bodysuit to license plate, soundlessly weaving through the streets like a figure out of an urban legend. Who is this “Headless Rider” on the jet-black metal steed!? And why does it seem like Mikado’s already gotten himself neck-deep in the insanity that is the norm in his new home!?

1st Arc: Durarara!! (4 Volumes)
2nd Arc: Saika Arc (3 Volumes)
3rd Arc: Yellow Flag Orchestra (3 Volumes)
4th Arc: Akane Arc (still ongoing)

An espionage seinen manga that takes place in the era of Cold War. Ken, Dr. Hattori and Rosa, three different characters are forced to team up in order to protect Sphere of Salvation, a new technological miracle that is capable of changing the course of history. Whoever holds S.o.S. and masters all its hidden forces, will rule planet Earth.

This is a 4-koma comedy about a young girl named Ichimatsu Kohina who got possessed by a low grade spirit called Kokkuri-san.

Nakahara Yukiko stumbles upon a class filled with supernatural students... Just what are these weird misfits doing in a human high school? NOTE: READ FROM RIGHT TO LEFT. ALSO MASSIVE ART-CHANGE AFTER THE FIFTH CHAPTER. 

When Masami's father died, he was told by his grandfather that he had to move out. In order to find a new place that he could live in for 80,000 yen a month, he asked his unrequieted love "Kagome" to look for a new place for him. But unfortunately, because of that, he has had to join the "extremely normal phenomena observation society" that she founded. And on top if it, there are rumors that things seem to "appear" at the things that the she finds.

Siscon. Power-phobia. Son of the great General Luccafort. Son of a general. Wether-crown. Fourth-in-line for succession. The titles, accolades, expectations, respect, and envy for DX Luccafort keeps coming. But all he wanted to do was win Marion's hand.
Landreaall follows DX, his sister Ion, and his bodyguard/brother Rokkou as they leave their home in the countryside and brace themselves to take on whatever their famous last name brings them.

The story begins with 4 masters who could mastered each of them: Fire, Water, earth and Air.Their power were linked and fought together against evils.But one day the jealousy and the dominance was in the heart of each of master and decide to be separated and by doing this broken the link.In the village of fire there is boy who believe again to the 4 masters reborn and fight together, he will do anything to see again the power of the link of the 4 masters.

One volume of dark supernatural short stories. Living spirits, oni, death, and reincarnation are some themes in these creepy tales.

A collection of short stories. Note that the vast majority of these stories contain heterosexual romance themes. A few stories explore transgender issues, but it's a stretch to call them shounen-ai or BL romances. This series demographic is josei.

Le théâtre de A
1.Oeufs D'ange - Tenshi no Tamago
A man is asked by a young painter to be her model.

2. Velvet Going Underground
A doll becomes a super idol. Hijinks ensue.

3. Childhood's End
Alastair runs away and meets the Rabbit.

4. Bite Me Something
Allistaire followed Mr. Rabbit all the way to Wonderland. Will he be able to find him among the crowd?

5. Long Along Alonging
A girl asks a vampire to be his apprentice. But what is her motive?

6. Till Dawn
In a dark tower, a caged voice is singing until a hunted man enters the darkness.

7. Leçon un
Sequel to Long Along Alonging.

8. My Skin on My Back

9. Highland Walker
Sequel to Leçon un.

10. Perfect World
The story of a young wife whose husband is infected with a fatal disease called Flower-Blossomitis.

11. Perfect Lady
Sequel to Perfect World and drawn especially for this book.

12-13. Looks Like a Teaspoon
A boy named Allistaire is often teased at his all-boys school. One night he dresses like a girl and stumbles upon the boy who often bullies him, Simon. Allistaire runs off into a tower and as Simon runs after him, we see the sign "Welcome to Wonderland" hanging by the tower's door.

14. The Pearl Blue Story
Do you believe in mermaids? Coggy, a young boy finds a mysterious lady laying down near the shore of the beach. He brings her home to help her.

15. I Am a Piano
A piano tells the story of her life and the people she encounters.

16. Parade

Le théâtre de B
1. Noël
A short story about a holiday romance.

2. Teddy Bear Satsujin Jiken (The Teddy Bear Murder Case)
Four murders have taken place at an all girl school. Lying beside each of the victim was a teddy bear with one missing limb.

3. Yonshimai Satsujin Jiken

4. A is for Alice
Alastair, a grown man, is off to follow the Rabbit once again to return to Wonderland.

5. Nedai no Musume Atelier no Musume (The Bedroom Girl, The Sculpture Room Girl)
A story about a girl in her death bed finding another chance in life in the body of a doll.

6. B&W (Black&White)
A story about a boy waiting for his sister.

7. Le Jardin du thé (The Tea Garden)
A mysterious story about a poor young man who orders a kind of tea called Huan Ying – “The Illusion”.

8-9. Free Fitting for Her
A priest and his captured vampire must save a naive and selfish young girl from the murderous desires of a Lolicon. But perhaps this girl isn't all that she seems.

10. Rose Dusk, Pale Moon

11. Hello, My Sister

12. The Happy Prince

13. Welcome to Wonderland
Simon, Alastair's old classmate, is now a grown man who bumps into his childhood Wonderland traveller.

In the near future, it is possible to instantaneously measure a person's mental state, personality, and the probability that a person will commit crimes with technology called the Dominator. Just thinking about a crime can make you guilty, and in this world there is no mercy for criminals.
Detectives work in pairs—one Enforcer and one Inspector—with Enforcers delivering lethal justice, and Inspectors making sure their partners don't take things too far. The story follows an Enforcer Shinya Kougami, who must solve and manage crimes in this dark future.

From MangaHelpers:

Meldina hates humans, and wants nothing to do with them. Since her parents' deaths, she has desired to live surrounded by machines, and everyone in town thinks she's a weirdo. One day, she meets a big machine that she names Machina and treats it as a friend. Her meeting Machina, as well as meeting a potential friend in a girl named Alisa, kicks off a series of events that bring to light dangerous secrets about herself and about her parents' deaths. [tethysdust]

Strange murders are happening in Tokyo. Due to liquid evidence at the scene, the police conclude the attacks are the acts of man-eating monsters, ghouls.
College buddies Kaneki and Hide come up with the idea that ghouls are imitating humans so that's why they haven't ever seen one. Little did they know that their theory may very well be reality.

Note: The prototype chapter won the Young Jump 113th Grand Prix award in 2010.

Yi Raeeum, a boy who is always conscious in dreams. A spectacle in a dream... a street in a dream... a life and death drama where the secrets of dreams and a fate following a young time intertwine.

Seikyou Private Academy, built on the intrigue of traditional occult myths, bears a dark past—for 60 years, it has been haunted by a ghost known as Yuuko, a young woman who mysteriously died in the basement of the old school building. With no memory of her life or death, Yuuko discreetly founds and heads the Paranormal Investigations Club in search of answers.

After a chance meeting leads Yuuko to cling to diligent freshman Teiichi Niiya, who can see the quirky ghost, they quickly grow close, and he decides to help her. Along with Kirie Kanoe, Yuuko's relative, and the oblivious second year Momoe Okonogi, they delve deep into the infamous Seven Mysteries of the storied school.

From The Pink Panzer:

In the year 2999, only eleven cities still survive on Earth. The climate has changed drastically, and a biochemical apocalypse has made women extinct. For centuries, the male population of Earth has survived by depending on only one woman, called the Holy Mother, whose ova are harvested to create genetically engineered children. By now, any concept of a world in which women exist as ordinary people is long gone. Society has re-structured itself around all-male families, and relationships between men and adolescent boys have become the norm.

At the beginning of Marginal, the Holy Mother is assassinated by a terrorist known as Grinja. The government in power doesn't want to start a mass panic, so it pretends that the Holy Mother has only shed her vessel, and that she will be miraculously "reborn" in the near future. The public, which is superstitious and devout, believes this easily. Only government officials know that behind the scenes, there is a frantic effort to create a being able to give birth.

The manga's story revolves around Kira, who becomes involved in a three-way relationship with Grinja, the aforementioned terrorist, and Ashijin, a young man who calls himself Kira's owner. A complex plot and flawless world-building make the story irresistible, and Kira's search for freedom is as symbolic as it is gripping.