Hey lunalover,
I am also currently writing an essay about mountain biking or biking in general for my perspectives class. These are some of the sites that I used for history....
http://www.moaa.org/magazine/february2004/f_steeds.asp <--good info about bicycles being used by the army in the 1890's.
http://www.mtnbikehalloffame.com/history.cfm <--the mountain bike hall of fame that several other people have mentioned.
If you want to "share ideas"
feel free to send me a message.