Peter Watts is right up there with Charles Stross for great intellectual hard Sci-fi. Both also have several books published under the creative commons license:

http://www.feedbooks.com/author/193 (Peter Watts, Starfish was a great biopunk marine biology novel)

http://www.feedbooks.com/book/228/accelerando (Accelerando, reccomended for anyone who likes Dyson Spheres, Post Human intelligence, Distributed Autonomous Organizations, and mind bending sex)