After seeing a lot of ideas and consulting my dad and father-in-law, I chose to go with an L shaped molding. It was 8' for only $6.50. It was 1"x1" L. I also picked up a 1/16" dowel (4' for $.25). So, the grand total for two 4' shelves was $7 (plus nails, glue and spray paint). I had the guys at the hardware store cut my molding in half for me so there was minimal work to do at home. I took some wood glue and glued the dowel along one edge, securing with clips until it dried.
Insert books and you're done!