Although the Library District Overdrive collection is constantly adding new titles, there are two other sites to search for free ebooks or to see if an individual title is formatted and available from a major ebookstore vendor.
Inkmesh is an ebook search engine and can also be used to compare ebook prices, search by subject and to locate free ebooks. Clicking on the about link will list the sites that are searched. Additionally, there is a link for promotional free e-books.
Freebooks: The site has ebooks in many formats which include public domain and original books. It is also an independent digital publishing house for ebooks uploaded by authors.