Recently I read an amazing hard sf book Blindsight by Peter Watts which unfortunately is not available in e-book form as of now, though the author may put it up at some point under cc license. However he has the first 2 books of his Rifters tetralogy free under cc license at his web site rifters.com, in html and pdf formats. They are very good also and I ordered the rifters 3-4 immediately from Amazon, again unfortunately not available in e-book form. The specific links are:
http://rifters.com/real/STARFISH.htm
http://rifters.com/real/MAELSTROM.htm
Liviu