There's yet another source of data that you can feed into Evernote; Kindle book highlights. As you read a Kindle book (which you can also do on an iPad or other device. You don't need an Amazon Kindle to read Kindle books) you can highlight parts that interest you. Just hold down your finger and swipe the area to highlight. You can highlight as many bits as you want. These are backed up to Amazon and you can see them on the Amazon web site. Once you have viewed them, you can use the Evernote web clipper to send them to Evernote.
This allows you to take clippings from books and add them to Evernote as reference material.