Recommendations

If you liked Usavich add

...then you might like Gyagu Manga Biyori add

A small package of senseless but fun animation, made of original joke with some historical references

If you liked Star Ocean EX add

...then you might like Zero no Tsukaima add

Character is taken from his/her own world to another full of magical and supernatural phenomenon and they grow and train in order to realize their destiny in this new world

If you liked Juuni Kokuki add

...then you might like Zero no Tsukaima add

Character is taken from his/her own world to another full of magical and supernatural phenomenon and they grow and train in order to realize their destiny in this new world

If you liked Rosario + Vampire add

...then you might like Elfen Lied add

Both of them have a lot of ecchi scenes and the main character from Elfen Lied has two personalities, the cute Nyuu and the mature Lucy.So does Rosario+Vampire:the cute Moka and the mature Inner Moka.

If you liked Umineko no Naku Koro ni add

...then you might like Higurashi no Naku Koro ni add

Same author, both question arcs adapted from the game. Creepy children, murder mystery, horror, everyone is a suspect.

If you liked Umineko no Naku Koro ni add

...then you might like Higurashi no Naku Koro ni Kai add

Creepy children, paranoia, mystery, AU. Same author, similar feeling, great story, great characters.

If you liked Nogizaka Haruka no Himitsu Pure Rezza add

...then you might like Nogizaka Haruka no Himitsu add

You have to see part #1!

If you liked Koi Kaze add

...then you might like Wicked Lessons add

if you watch them both, you'll find them to be very similiar. Even if wicked lessons is a hentai, both deal with incest anyways. The sibling love story is presented in a nice way in each although they end up with different consequences.

If you liked Death Note add

...then you might like Ghost in the Shell: Stand Alone Complex add

Dig out your sleuth hats. Both series follow a plot that is very challenging to figure out. While Ghost in the Shell has a greater focus on action, Death Note and GitS share the ability to baffle with plot twists and complex schemes.

If you liked Moetan add

...then you might like Isshoni Training add

From the surface, both show looked educational and profiting.

If you liked Witchblade add

...then you might like Variante add

Similar concept with monsters arms being attached to the main character which then makes them more violent. The main characters are also similar both female and the monsters attack/kill their families.

If you liked Variante add

...then you might like Parasyte add

A parasite attaches itself to the mains character arm which then gives them the strength that they then use to fight and kill other parasites.

If you liked Cromartie High School add

...then you might like Gintama add

Gintama is a mix of the past and future, while Cromartie High deals with present day life. However, both animes are hilariously exotic and whacky, pushing the limit of random episode plots. Both animes also show off a bigger cast of main and sub characters. If you're looking for comedy, look no further.

If you liked Yankee-kun to Megane-chan add

...then you might like Hot Milk add

Tough guy + crazy cute girl = "how did i get into this?!"
From what i remember, Hot Milk is more on the old school/ecchi side, but hey - I'm not complaining.

If you liked Pandora Hearts add

...then you might like .hack//SIGN add

There's a similar atmosphere in both of these animes - at the same time tense and playful. Both stories drop you into the middle of things and give you one piece of the puzzle at a time, as well as having a similar trio of main characters. There's a certain darkness in the background in both; a sinister something which we only catch glimpses of at a time, but which moves behind the scenes and may have power for either good or evil.

If you liked Fujoshi Kanojo add

...then you might like Tonari no 801-chan add

Tonari no 801-chan helped inspire Fujoshi Kanojo and offers a slightly less crazed fujoshi lead (don't let the green monster fool you!). Tonari no 801-chan is more comedy based and less romantic. However, Fujoshi Kanojo's romance can be hampered by the girl's over-the-top behavior.

If you liked Ergo Proxy add

...then you might like Neon Genesis Evangelion add

Same post-apocalyptic concept, just everything is in a much smaller scale in terms of setup, characters, and story. Both series stress on character emotions and questions of morals, focusing more on the psychological developments rather than action, yet it is all laid out in a very advanced science fiction background. You also have the god-like rulers who debate amongst each other in monotone voices without significant physical features.

The stories are paced the same, really the key difference is that the focus is not on children and many of the similar extreme questions and psychological challenges are presented in a much subdued and more subtle manner.

If you liked Zegapain add

...then you might like RahXephon add

Both are sci-fi with lots of mecha battles and very similar in their conflictions on what is reality and what is not. Rahxephon has enclosed spaces separate from the outside world where people live oblivious to the actual situation outside of these zones, in which humankind is battling the enemy. They are similar in appearance to the Deutera areas but conceptually like the quantum servers in Zegapain. Also in both anime the enemy appear human though they are not. The main character is in both cases a male and have a love interest.

If you liked Lucky ☆ Star add

...then you might like K-ON! add

both animes are about skool girls
and they are both really funni

If you liked Saki add

...then you might like Taishou Yakyuu Musume. add

In short Taisho Yakyuu Musume is Saki set in the 1800s with baseball instead of mahjong.
The two series share lots of similarities from a wonderful and diverse cast of girls (a girl for everyones particular fetish lol) to a slice-of-life school club setting with some srsbiz competition going down. Thats only my impression after seeing the first episode of Taisho + some promos and following Saki anime/manga since it started in April.

If you liked Furi Kuri add

...then you might like Dead Leaves add

If your into chaotic action and humor with an underlying story of epic proportions then you would be well served with either series.

If you liked Furi Kuri add

...then you might like Tengen Toppa Gurren Lagann add

Classic Gainax. From story and style to bizarre mecha and over the top action, both series share a similar epic quality amidst the chaos.

If you liked Furi Kuri add

...then you might like Shikabane Hime: Aka add

If your into the art style of FLCL then you may like another Gainax series; Shikabane Hime. You'll notice immediately the similarities in style.

If you liked Ai to Yokubou wa Gakuen de add

...then you might like Kamisama no Ude no Naka add

One takes place in an all-boys catholic school, while the other one is a school that taught the students everythings about sex.

Both are yaoi mangas that got smut.
And both are similar in the fact that those are series of stories revolving around the students, teachers, and staff.

Student X Student ; Student X Sensei ; Sensei X Sensei...

If you liked Witchblade add

...then you might like Devilman Lady add

Devilman Lady and Witchblade look at the evolution of man into monsters, though Witchblade looks at it through a more technological way as opposed to Devilman Lady which is solely supernatural.

They both feature adult female lead characters who transform against their will into tough, blood-thirsty, "monster-like", feral fighters. The protagonists of each anime have important reasons for fighting, though they are different, as one fights to find her true identity as a person or a beast (Devilman Lady) and the other fights to protect and take care of her daughter (Witchblade).

Violence, sexuality, adult life, government conspiracies and the unbridled lusts for raw power are explored thematically in both anime as well.