Project Guttenberg is a great place to acquire free public domain ebooks. The project recently made accessing its catalogue of 42,000 free ebooks much easier by adding Dropbox integration.
All you have to do is find your favourite ebook and click the Dropbox icon next to it, and that book will be synced to your Dropbox. That means you essentially have one click syncing for all the books you care to read from Project Guttenberg. Kindle users will have to go a step further and email the file to their Kindle email address, but it's nothing you couldn't automate with Wappwolf. Hit the link to read more.
Download Project Gutenberg ebooks to your Dropbox [Digital Inspiration]