OpenCulture, a great resource for lots of things, has a great list of free science fiction classics available online, in both text and audio formats.
The books include classics from Asimov, Huxley, Orwell, Orson Welles, and even the Chronicles of Narnia.
This is a great resource for teachers and students to get free copies of the books, and the audio books can help ELL and struggling readers.
Related:
Other resources from Open Culture
