Also good is the "Baen Free Library", a free e-book site started in 2000; the library has been growing slowly ever since. www.baen.com/library/

Most of the books were previously published by Baen, generally  the first book or two of trilogies and series.  Originally the site directly offered free downloads with no registration, in several different formats.  Looks like they've moved the downloads to "webscription.net" but have kept the no-registration and choice of formats.

The "Librarian" is Eric Flint, who also offers free e-books of certain of his novels, in PDF format ,on his own web site.

Thanks for the heads-up about fictionwise.

If we're talking free e-books, I highly recommend Project Gutenberg. It's so useful that I'm always surprised that people haven't heard of it. Now you won't find any recent sci-fi since it's all texts that have entered the public domain, but there's some great (and kooky) classics. For example, Edgar Rice Burrough's John Carter of Mars series.

http://www.gutenberg.org/

And the science fiction 'shelf':

http://www.gutenberg.org/wiki/Science_Fiction_%28Bookshelf%29