Check out the following URL:

http://www.gutenberg.net/cgi-bin/search/t9.cgi

This is a little bit like the Gnu project. Volunteers are scanning old novels with expired copyrights into digital form. Examples of SF authors include:

Jules Verne
H.G. Wells
David Lindsay

I looked unsuccessfully for more modern authors like: Heinlein and Panshin. Wells and Verne are fun to read if you're just getting started with Science Fiction (they're a bit dated). Lindsay is one of my favorites but he's hard to get into and not recommended for people just starting with Science Fiction. If you chose to read Lindsay's "A Voyage to Arcturus", stick with it until you reach the planet Tormance. The novel's style changes radically after you get there and it becomes a fun read.

Gary