for beginners I'm not sure, but http://www.mangahelpers.com is supposed to be a very good resource. I don't really read manga myself so I can't talk from personal experience. I just remembered a friend suggesting this to me. I took a peek at a series I like and it had furigana so I'm sure you'll find something you can ease yourself into.
The only two mangas I have are Love Hina and Berserk. Love Hina seems like it'll be decent reading practice since it has furigana and the dialogue is pretty light, but Berserk will probably take me quite some time before I can even attempt it. I've only been studying Japanese a little over a month now, and Berserk is very, very dark, and the dialogue is much weightier, not to mention there are a lot of foreign concepts due to the heavily medieval theme that probably don't translate themselves too easily.
I mostly bought these for myself as a self-bribe to study hard, along with some other random stuff. Thus far I haven't really seemed to need them, though, and have been quite dedicated. It bodes well. Hopefully in another few months I can start attempting to actually read something a little bit at a time. I can already skim through Love Hina and pick out various words I know, and occasionally pick up on something with those few words plus context, but it'll be a good while yet.
EDIT - I should clarify: these are the only two mangas I have in Japanese. I'm far from an otaku, but I do have a few English series laying around. =)