My bookshelves are a total mess, but I have an organizational system...sort of.
The top shelves ( in my four stupid bookcases, I just need one giant one haha) are the books that I re-read most often, i.e. the fountainhead, the awakening, mama day, rebels angels, a farewell to arms, and short story collections or poem collections.
The middle shelves are organized by author; Vonnegut, Palahniuk, Leguin, Dawkins, etc.
The bottom shelves are my reference books (I also have a bookcase for other assorted references, mostly text books from different classes) which are mostly dictionaries ( It is important to have more than one!) rhyming dictionaries, my grammar bibles, some non fiction like Gendered Lives (I am a feminist lit major, go figure) and How to Read a Poem, How to Read a Book.
In front of those are the books that didn't fit anywhere. My floor has the books I have yet to read, right now its Suite Francaise, Portrait of the Artist as a Young Man, Sargasso Sea, Mansfield Park and Guns Germs and Steel.
I keep my jewlery tree ( weird I know) on top of Bookcase number 1 along with my incense and some rubberbands, my other three have papers, mail, cds, old notebooks, pens, and other assorted junk on top! haha
H.M. Rush
"A mans errors are his portals of discovery" - James Joyce