If you're looking to get started with e-books and want to start reading free e-books, check out these links for free e-books. Most e-books are available free because the copyrights have expired, or are designated from the publisher.
If you're interested in searching for titles through Google Books, you can do it here:
If you're unsure of what e-book format is compatible with your personal e-reader, or if you want to know what devices you can use to read a particular file format, check out the Comparison of E-Book Formats from Wikipedia that details all formats available and covers virtually all devices. Wikipedia is updated frequently, so check back often!