I would add Ben Bova's Grand Tour series, where he writes on human colonization of the solar system.
I haven't read them all, as there are quite a few (cf
http://en.wikipedia.org/wiki/Ben_Bova#Grand_Tour), but I have liked a lot the ones I read (Mars, Return to Mars, Saturn, Jupiter, ...).
I've had a quick look, I can't seem to find those ebooks on legal sites, though.
A few of his other works are available on Baen or Fictionwise.