I'm not much into manga and thus haven't read it myself, but I've seen a lot of recommendations for よつばと！ as an excellent manga for learners, as it uses very everyday language while remaining funny and engaging. I don't know any titles off the top of my head, but I imagine you'd also do well with anything with a school setting - setting aside all the fantasy/shounen manga, stories with younger protagonists tend to be easier to follow.
I jumped more or less right into general fiction myself (and if you're brave, I can recommend some easy general-audience authors) but I am very fond of 森絵都 for children's literature. I'd say her debut novel, リズム, is about a 5-6th grade reading level - it's a chapter book, but it's not too dense or full of kanji. カラフル is a full-length novel and somewhat harder, but even reading it as an adult, it's one of my favorite Japanese books.
Breaking into Japanese reading through "light novels" also seems to be popular. Personally, I don't think they're necessarily easier than general fiction, especially given the higher incidence of fantasy/sci-fi elements, but they're often more episodic and they do tend to come with a lot more furigana, so if you don't mind using a dictionary that might be an option. キノの旅 is supposed to be a fairly learner-friendly series.
Finally, if you'd like some nonfiction reading, there's always [url=http://www3.nhk.or.jp/news/easy/]NHK News Easy[/url]!
