Rogers Commission Report. Why the Challenger accident happened. See also the Federation of American Scientists Challenger Page with lots of related information. I particularly recommend the Feynman appendix to the report.
Commercial Space Markets. From current markets like communications to more speculative/long-term ones like helium 3 and asteroid mining, a brief summary of each market.
Kraft Report. How to reduce shuttle costs. This is the most detailed description of "shuttle privatization" which I have seen.