SpecFicWorld has magazines and eBooks available in the pdf format.
Project Gutenberg has a Science Fiction Bookshelf with loads of old scifi for free downloading. All their downloads are free of charge and free of DRM.
SciFiMatter.com I have not downloaded anything here but it comes up in search engines.
InkMesh, I have not downloaded anything here but it comes up in search engines.
ManyBooks.net, I have downloaded from here and it went seamlessly.
Fictionwise, I have downloaded and it worked ok. It is a division of Barnes&Noble.
MobileReads, I have signed up but haven't downloaded anything yet.
Smashwords, appears to have a fair number of DRM free books. Also seems to have a wealth of cheesy, sleazy stories.