If you liked
Natsu no Arashi!
|
...then you might like
Arakawa Under the Bridge
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Extremely similar animation style (the borders used in various frames are direct clones), similar episode pacing, same genre (supernatural romance comedy), same production company, same director, same sound director, same script writer, 3 of the 10 seiyu in NnA appear in AUtB.
If you liked
Speed Grapher
|
...then you might like
Darker than Black: Kuro no Keiyakusha
|
Similar theme, atmosphere, metaphysics governing supernatural powers, story progression and pacing. Both shows take place primarily in a "dark" city controlled by the underground where the main character fights against an omnipresent shadow-organization, filled with various goons who've derived powers based on their character flaws, in order to protect the freedom of a sheltered girl. The theme of science causing god complex is central to either story. The music used in both also strikes me as similar in style, composition and atmospheric use within the anime.