Uzumaki said:
Watch out though, because kids might want you to get a Go board after that.
Oh, and I missed the part where you explained why that was a bad thing.
Seriously, Hikaru no Go is an excellent manga, very accessible and quite appropriate for the age group in question. However, only the first volume is currently available. The second volume is due out this month, however.
Most of the others are great manga, but I'm not sure whether or not you would consider them appropriate for a school library or not. One Piece is a very funny manga, but like Naruto and others, has its share of violence. One Piece is more comical and farce, while Naruto has more in common with Dragonball Z (much heavier emphasis on fighting, later on). In the same vein, Shaman King is qutie fun, too.
Kare Kano (aka His and Her Circumstances) is good, but I've heard the later volumes get a little...odd.
InuYasha is a lot of fun...but has nudity and violence (although usually it's against monsters, and there isn't actually much in the way of sexual situations, other than comic nudity and groping).
Fruits Basket is popular, from what I hear, but I've never read it.
In short, all of the suggestions are good, depending on the leeway you have.