The Official Sites
NASA
JPL
The Mars Society
The Planetary Society

If your computer is set to run one of those silly flying toasters things, or a maze, or whatever, maybe you should think about doing something usefull with all of that processing power.  After all, when you computer is "sleeping", the processor is usually running overtime to draw all of that stuff.  Instead, how about crunching some data for UC Berkeley's SETI@home project?  The program is a screen-saver, and only runs when your normal screen-saver would run--while your computer is otherwise not in use.

NASA design studies (that never made it)
One of the most interesting activities of NASA is their summer research groups, where they pull(ed) together a large number of professors and the like to attack various long-range planning problems, such as building a serious space station.  As far as I know, none of the proposals made by these groups was ever put into action, mostly because they were extremely grand projects which did not lead where NASA wanted to go, or Congress would fund.  However, most of them are quite complete design studies which have not gone out of date, but are rather more possible now with current technology.  It can be expected that someone will eventually pick up these free design studies and run with them, given different motives than a governmental agency primarily interested in "pure science" and constrained by Congressional budgets.
10,000-Occupant Space Station
Self-Replicating Moonbase
 

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