Getting frustrated with constantly finding 404s on NASA and other space sites, I'm logging the ones I find here as of August 12, 2009:
404: http://lunar.arc.nasa.gov/status/1998/02261600.html
Found on: http://lunar.arc.nasa.gov/dataviz/index.html & http://lunar.arc.nasa.gov/dataviz/instrumentsd.html
502: http://clickworkers.arc.nasa.gov/hirise
404: http://www.nasa.gov/centers/marshall/pdf/166643main_MinimumSystemRequirements.pdf
Found on: http://science.nasa.gov/headlines/y2007/images/explodingeclipse/faq.pdf
Not loading: http://atl.calpoly.edu/mailman/listinfo/cubesat
Found on: http://cubesat.atl.calpoly.edu/pages/workshops.php
404: http://deepimpact.umd.edu/amateur/
Found on: http://research.dynamicpatterns.com/amateurscience/
changed March 2