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I like Arena37c
http://www.ongakusenkasha.co.jp/arena/ar_index.html

There's also CURE, FOOL'S MATE, (both having to do with visual kei)

What's In?, R&R Newsmakers, Rockin' On Japan, H, PATI-PATI

for Japanese Idols (includes stuff like Morning Musume, etc.)
Myojo, Kindai, Wink Up, Potato, Duet, JUNON, POPOLO


CD DATA (has extensive info on latest releases)
De-View (an information magazine about auditions for the show business)


I know http://www.cdjapan.co.jp/index.html should have them

YesAsia has some of them (I know they have FOOL'S MATE as far as J-pop Magazines go)