Rand Simberg (Transterrestrial Musings) gives a history of efforts to redirect NASA, and an alternative blueprint for the future, in a long essay in The New Atlantis ("A space program for the rest of us"). If you're interested in the recent trajectory of the agency, the Constellation and Ares projects, and what's been going on since the Obama transition, it's a good overview.
On the topic of future directions, Simberg accentuates affordability and sustainability. Much about the need to develop a propellant infrastructure based on low-cost launches, to enable lighter manned and other high-value missions.
In this space-refueling infrastructure, propellant would be cheaper, flight hardware wouldn’t have to be as heavy, and alternative launch vehicles would flourish. Every year that we starve the kind of research and technology that would make this possible and instead spend our money on mega-launchers like the Ares V is another year that we delay developing a truly sustainable space transportation infrastructure—and becoming a truly spacefaring people.
I would add space-based solar to the mix (particularly as applied to lunar propellant manufacture, but also for ground transmission). I'm pulling for SpaceX.
UPDATE (2009-07-24): A reader suggests that Simberg hasn't gone far enough. Simberg mentions that LOX is around the price of milk. A railgun might put a kilogram into orbit at very low cost; given the ability to coordinate microsatellites in orbit, small 1 kg tanks can be manouvered into large refueling stations.
Oh, and of course nuclear propulsion systems would provide a vastly more efficient solution than most of these ideas. But that would be wrong....
