Do you have more books than shelf space? Give yourself some extra storage space by installing standard-and-bracket shelves. Installing these types of shelves is very easy, and won't take much time. You'll spend more time rearranging your books than actually installing the shelves.
I wanted to put all of our various books and magazines in one spot to start on my eventual goal of having a multiple story library, complete with ladders, spiral staircases, and secret doors. Here's a motivational picture I took of the library in a monastery in Lima, Peru.
I already had a few hand-built bookcases, like these, but I needed more space, and I wanted them attached to the wall.