In digging around a little, I found a few good resources. I would love to feature some great book displays you've done in this blog, too. People love to see (and borrow from) other people's ideas! Please send in a photo of a favorite book display and I'll put it in the blog.
Here are the resources I found that I thought were helpful:
Twenty Rules for Better Book Displays (an article in Novelist's newsletter, this is geared toward adult displays but has some great suggestions.
So Tomorrow is one of my favorite youth services blogs, and this is a collection of display ideas
Our own Kathy Larson from Bloomer has posted some of her book display ideas on her fabulous blog, From the Short Stacks.
We have a relatively recent book in our professional collection (available on MORE) called DIY Programming and Book Displays by Wisconsinites Amanda Moss Struckmeyer and Svetha Hetzler.