I'm not a huge SciFi fan to begin with, but I happen to know that the Baen Free Library is an excellent resource for free SF ebooks. The rest of the Baen site has pay books.
Oh, and who doesn't love Fictionwise?
I started this as a new thread so people could post their favorite SF links here, too. so please add yours!
The best source ( IMHO ) is the usenet : alt.binaries.e-book.palm
Have a look, you wont be disappointed...
Yeah, but those are pirated, illegal copies of e-books...not public domain (for the most part). To each his own, as far as downloading warez files, but just wanted members to be aware that alt.binaries.e-book.palm is a mostly-warez newsgroup.