If you liked
Toaru Majutsu no Index
|
...then you might like
Campione! Matsurowanu Kamigami to Kamigoroshi no Maou
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Similarly styled battle shounen series.
If you liked
Gintama
|
...then you might like
Binbougami ga!
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Same director, exact same style of humour and show.
If you liked
Koukaku Kidoutai
|
...then you might like
Kara no Kyoukai Movie 1: Fukan Fuukei
|
Both GITS and KnK explore themes of humanity and further extensions of humanity; they also share similar protagonists (Motoko and Shiki are alike in personality and appearance), the soundtrack is also similar in style.
If you liked
Higurashi no Naku Koro ni
|
...then you might like
C³
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Both start off as cute moe comedies before switching to a horror style.
If you liked
Nurse Witch Komugi-chan Magikarte
|
...then you might like
Higurashi no Naku Koro ni Kira
|
Both series deviate from more serious parent stories to produce self-parodies (and parodies of other things). Both series also feature magical girls and fanservice.
If you liked
Shakugan no Shana
|
...then you might like
Mahou Shoujo Madoka★Magica
|
Both series share a similar plot, in the sense that there are magical (or supernaturally powered) girls fighting monsters which feed upon people. Madoka is rather more refined than Shana though.
If you liked
Azumanga Daiou The Animation
|
...then you might like
Morita-san wa Mukuchi.
|
Morita-san has a similar style of "realistic" slice-of-life comedy, and is presented in short episodes (much like Azumanga originally was).
If you liked
Lucky☆Star
|
...then you might like
A-Channel
|
Lucky Star and A Channel both share similar writing style and artwork, and both are extremely funny slice of life series to watch.