Electronic Books Organized

I have a lot of electronic books, both on Kindle and my iPod. I kept the order on my Kindle for a while, but a couple of years ago I started putting them by author in a little notebook. That worked, but became disorganized as an author outgrew its allocated space. So I'd have another author in the middle of an author's output. So I bought a box to hold index cards and started transferring authors onto index cards and putting them in alphabetical order. To add to one, I just have to find the last index card to see if there is space on it. If not, I can start a new card and not have to worry about it lapping into another one.