If you liked
Hayate no Gotoku!
|
...then you might like
Zettai Karen Children
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Both are wacky over-the-top comedy anime that don't take themselves too seriously. They're done by the same studio, so the animation is very similar. You might also hear some of the same seiyuu, and the soundtracks are composed by the same person.
If you liked
Speed Grapher
|
...then you might like
Mnemosyne: Mnemosyne no Musume-tachi
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Both are neo-noir mystery anime dealing with erotic grotesque visuals, supernatural powers, and just give out the same vibe in general.
If you liked
Animal Yokochou
|
...then you might like
Doubutsu no Mori
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Both are lighthearted funny anime for kids (mostly girls I guess) with a girl main character accompanied by (stuffed) animal friends.
If you liked
Rekka no Honoo
|
...then you might like
MÄR
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Both from the same creator and VERY similar. Both stories are focused around tournament fights and special weapons. MAR seems to be geared towards a younger audience, though.
If you liked
Kimi ga Nozomu Eien
|
...then you might like
Kanon (2006)
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Both are sad romance anime based on H-games. Kiminozo is a bit more serious that Kanon is, though. Kanon is a bit more... magical.
If you liked
Maria-sama ga Miteru
|
...then you might like
Strawberry Panic
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This one is easy. They're both set in a Catholic all girls school and share the same themes like yuri and sisterhood relationships. Strawberry Panic takes the yuri a bit more further, though. I think the anime's demographics might be different. Marimite is definitely meant for girls, not sure about Strawberry Panic.
If you liked
Love Hina
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...then you might like
Rikujou Bouei-tai Mao-chan
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The anime are both by the same creator (Ken Akamatsu) and have the same character designs. The anime don't really have much in common aside from that. But there are some cameos and references to Love Hina in Mao-chan, which can make it more fun.
If you liked
Texhnolyze
|
...then you might like
Serial Experiments Lain
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These anime share many of the same key staff. The first thing you'll notice are of course the character designs, which are done by Yoshitoshi ABe. Both anime also share the same themes.
If you liked
Tsubasa Chronicle
|
...then you might like
Cardcaptor Sakura
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Both are CLAMP anime and are full of cross over characters. If you've seen CCS first, you'll definitely enjoy Tsubasa Chronicle more. The other way around... Probably makes it a bit harder to recognize characters. The genres are a bit different though. CCS is magical girl anime whereas Tsubasa Chronicle is more the adventure type.
If you liked
School Rumble
|
...then you might like
Azumanga Daiou The Animation
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Both are high school comedy anime. Azumanga Daioh is a bit more wacky and random, and School Rumble has more story (just a little), but if you like one, you should also like the other.