Official Google Blog: More books in more places: public domain EPUB downloads on Google Books

Try doing a search for [Hamlet] on Google Books. The first few results you'll get are "Full View" books — which means you can read the full text. And, because the book is in the public domain, you can also download a copy of Hamlet in PDF form.

Starting today, you'll be able to download these and over one million public domain books from Google Books in an additional format. We're excited to now offer downloads in EPUB format, a free and open industry standard for electronic books. It's supported by a wide variety of applications, so once you download a book, you'll be able to read it on any device or through any reading application that supports the format. That means that people will be able to access public domain works that we've digitized from libraries around the world in more ways, including some that haven't even been built or imagined yet.

My format of choice for download is PDF - especially if there are illustrations, but it's nice to know we have choices.