I LOVE this tumblr of book collections, called "Book Lovers Never Go to Bed Alone." It's got scads of photos of peoples' libraries, from artful and quirky to elegantly Martha Stewart-ish to metal-shelves-in-a-garage-ish.
It's perfect for book storage and display ideas, particularly if you've got your own out-of-control collection. Between JB's sci-fi/fantasy series (which have like a million books each) and my classics/historicals/mysteries, plus every book I ever read in college as an English major - um, lots - we've already outgrown the shelves we've got.
I seriously wish we had a non-functioning fireplace (or a fireplace at all). Sigh. How do you store your books?