I have always like putting my books on shelf for me to see if I need to access them or make move things around a bit. The hardest part is finding the right kind of shelf and this shelf is nothing short of simple and great, you install two metal plates and use the first book as the start of the shelves. It can support up to 15lbs (6.8 Kgs) and stack up to 16 inches(40 cm) for only $15.

Link: MoMa