As mentioned above, http://www.panam.com
is probably the best one, as it is the most comprehensive about the original
Also, you might want to check out http://www.panamair.org
And if you want to read about the history of all three incarnations of Pan Am, check out http://www.panamhistory.com/
. For Pan Am Air Bridge, check out http://pages.prodigy.com/jttoad/abridge.htm
, and for the Pan Am II news archive, check out http://pages.prodigy.com/jttoad/pan_am.htm
Hope that helps!