Some of them looked fantastic, but seem like they might damage the books, especially paperbacks, over time:
Others were very artsy and chic, and I could almost see them in my house (even though I'm not very chic at all):
This "storyline" shelf by Frederik Roije represents the soundwave created by speaking the word "bliss." How appropriate is that?
This equation bookshelf from estudio breder would make a great gift for my sister, the math major:
Any shelves that hold books on a diagonal would drive me bonkers, I think. They kind of make me go cross-eyed, and I know my anal-retentiveness would kick in and I'd spend all my waking hours arranging and rearranging and trying to get everything to look just right:
These aren't really my style, but I think they're pretty cool:
These, I love. These I want in my house RIGHT NOW, please:
This is a wicked cool idea. Probably wouldn't work in my house, but I dig it:
As far as how to arrange books on traditional shelves, I'm glad that a lot of design sites recommend mixing traditional side-by-side arrangements with stacking books. It saves space in a big way, and also creates a little bit more visual interest:
I also love the recently popular trend of arranging books by cover color to create a rainbow effect. I don't think I'd be able to do it if it required breaking up series or sets, but I love looking at photos of other people's efforts:
There's an entire Flickr pool devoted to spectrum shelves.
Here's the original bookshelves post.
Edited to add: one of my message board friends posted this the other day, and I cannot believe that something so awesome is in the world. Library built into a staircase: