Sony says that over one million public-domain books are now available for their e-readers (PRS-505 and PRS-700). Sony is using Google's Books project for these books, which are available in EPUB format.

Amazon has over 300,000 titles in their Kindle store, and Barnes & Nobles, which recently announced their own online bookstore, has over 700,000 titles, out of which more than 500,000 are public domain, also powered by the Google Books project.