A few more places to find books.

Bookyards – unfortunately, these seem to be limited to what you could find on Gutenberg, and they are in PDF.

Mobipocket – at least these are in .mobi format.

Baen – they’ve done a lot of their back catalogue.

Bookmonk – interesting site, graphical links, for those who choose books by cover.

Smashwords – new publications, many free.