They are none other than $3.99 spice racks from Ikea (the Bekvam). Each one is 16.5 inches long which is terrific for small rooms. If you don't live near an Ikea, keep your eyes open at thrift shops, garage sales or dollar stores.
Visit Lillian at Domestic Simplicity to compare this book display to her other book shelf and also to smirk at "the chaos that ensues around and behind me when I try to spend 10 seconds just taking pictures of some bookshelves." (And you may recognize Mia and Nick's lovely room from our Small Kids, Big Color contest.)
(Image: Domestic Simplicity)