Ring is probably the scariest manga I've read (I've not really found any really scary mangas yet though...) but doesn't quite have the same effect as the film (naturally). However its a hell of a lot scarier than the original novel. Pet Shop of Horrors isn't really that scary, but I guess it depends on how easily you are scared...Ring 1 and 2 are on www.mangareactor.tk (if you have edonkey) so you can download those there if you want to try it out...