Plenty of books available for it and you can always convert your own books and use a USB cable. I had some PDFs and it was as easy as just emailing my Amazon's kindle account. It cost 10 cents, but converted it into the kindle format and sent it to the kindle for me. You can do it free if you want to transfer it to the kindle yourself.
Read through this for more info:
http://brentnewhall.com/Kindle_Fan_Guide.pdf