A friend sent me a link to floating bookshelves as a joke... and I bought them.They are awesome! They are tiny little L-shaped pieces of metal that you can't even see once they're up. You put the back cover of the bottom book under the bottom of the shelf and it clips into a tiny lip on the shelf. Voila floating books!
(The corner before the shelves)
(The corner after the shelves)
They hold up to 15 lbs. of books and I actually have a tiny bit of space on my bedside table again!