Over one million public domain e-books from Google are now also available in the standard EPUB format.
Here's an excerpt from the announcement:
I'm excited to announce that starting today, Google Books will offer free downloads of these and more than one million more public domain books in an additional format, EPUB. By adding support for EPUB downloads, we're hoping to make these books more accessible by helping people around the world to find and read them in more places. More people are turning to new reading devices to access digital books, and many such phones, netbooks, and e-ink readers have smaller screens that don't readily render image-based PDF versions of the books we've scanned. EPUB is a lightweight text-based digital book format that allows the text to automatically conform (or "reflow") to these smaller screens. And because EPUB is a free, open standard supported by a growing ecosystem of digital reading devices, works you download from Google Books as EPUBs won't be tied to or locked into a particular device. We'll also continue to make available these books in the popular PDF format so you can see images of the pages just as they appear in the printed book.