Of all the gifts I've ever given, one of my favorites is a old dynamite crate I found in an antique shop. I gave it a coat of clear gloss and it looked so fabulous that I eBayed one for myself, and it now sits in my library. And although I don't use it for book storage, since one crate wouldn't go far, it's really cool to see what an array of crates can do. They make for a lovely visual and are sturdy to boot, something modern bookcases tend to lack.
If your book collection's a little on the expansive side, then you might want to take a look at this for ideas. That's 54 crates, in case you were wondering.