Free Book Spot is pretty good for ebooks but it depends what you're looking for. You're probably not going to get brand new titles, but there's loads of stuff from classics to more recent novels.
You don't need to register to download anything and the downloads are usually zipped files with different formats inside - most common are epub, pdf and mobi; but some also have rtf, lit and lrf formats as well. You can search by author, title or you can flick through the categories until you see something you want.
I've been downloading a few books (the Dexter series) and haven't had any problems yet, and the books look pretty good (ie: full copies, no missing pages, no dodgy scanned photocopies). The link is below.
http://freebookspot.me/Default.aspx