A couple of very useful links to free SF/Fantasy (and other genres)
http://finding-free-ebooks.blogspot.com/
http://online-novels.blogspot.com/20...e-fiction.html
Cory Doctorow is also well worth a look as are some of the very talented guys and gals that reside here on MR.
Simon Hayes is very funny. His first in the Hal Spacejock series is here (free)
http://www.spacejock.com.au/Hal1Download.html and the rest are very reasonably priced.
The best though is Philip K Dick. Unfortunately his works are not available free (legally). I would recommend "Flow My Tears The Policeman Said" as a starting point.