In relation to anime music, I wouldn't say I am that into J-Pop or J-Rock by itself.
Although I like male singers I have come to a realization that my top 3 are all female singers
Maaya Sakamota
Who doesn't know Maaya, from her first main role as Hitomi in Escaflowne at age 15 we have been subjected to her beautiful voice. She also worked with Yoko Kanno one of the best anime composers there is
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New Opening for Tamayura
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Ao No Ether~ Macross Frontier
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Hemisphere~Rahxephon
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Plantium/I am a Dreamer~Card Captor Sakura
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No Need for Promises~Escaflowne (best Opening ever)
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Hikari no Nake e~Escaflowne (my favorite of the many insert songs)
Nakagawa Shouko
Probably my favorite new artists in the last few years. She is also a total anime fangirl which I think is awesome
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Sorairo days~ Gurren Lagann
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Happily Ever After~ Gurren Lagann
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Ray of Light~ Fullmetal Alchemist Brotherhood
Ritsuko Okazaki
Such a sweet beautiful voice. When she died I think we lost something very unique
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For Fruits Basket~ Fruits Basket Obviously
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Chiisana Inori~ Fruits Basket
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Serenade~ Fruits Basket
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Morning Grace~Princess Tutu
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Although My Love is Small~ Princess Tutu
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I'm Always Close to You~ I believe this is from the Visual Novel Symphonic Rain
Note: My appreciation for the songs does not necessarily mean the anime series are favorites: Although as series I am extremely fond of Escaflowne, Gurren Lagann, Fruits Basket, and Princess Tutu.