the sun and the moon and the stars

So, I just got my iPad (well, yesterday) and I'm busy loading it up with content both fannish and otherwise.

I love it oodles, but there's one issue I have with it, and it's the same issue I have with the Kindle - I can't organise my ebooks hierarchically. As well as actual ebooks, I want to upload a bunch of fic saved as ebooks, but I want to sort them in folders and navigate them thusly, instead of one flat list.

iBooks, although it's a nice app, doesn't allow for a hierarchical system, and it's what I'm using for my actual-book ebooks. So, what I need is another decent epub-reading ebook reader app, preferably one that allows hierarchical sorting (or heavy tag usage). Any recommendations?

(Also, any recommendations for other nice apps are welcome!)

(Crossposted!)