Librarything is my favorite way to track my books. It's an online cataloging site that started out just for books, but now can also handle comics, music and movies, as well as stuff I probably don't even know about. The website is really easy to use. A lot of member participation has gone into building the site. It's a fun place for a certain kind of person.
They used to sell CueCat barcode readers to make it easy to add your stuff. There has been an Iphone app and a mobile-friendly site for quite a while. But now they have a free Android app that includes a barcode reader. They are also giving FREE LIFETIME MEMBERSHIPS to anyone who gets the app and logs in. I'm jazzed about the app because this mean it's easier to check my library to avoid buying duplicates when while I'm out hunting used books. I spend far too much money "saving money" on books.
However, I think the lifetime membership is a really good deal. They were only $25 when I got mine, I don't know what they cost now, but you get unlimited entries with it.
You can get app at Google Playstore
https://play.google.com/store/apps/details?id=com.librarything.librarything&hl=en