Triumph of the Nerds is inspirational and makes you feel like geeks can make something out of nothing.

Ken Burns' documentary on Frank Lloyd Wright makes you feel like you identify with a singular drive for vision above all else (The SC Johnson headquarters in Racine, WI are heavenly but the roof leaks buckets)

Not truly a documentary but "My Architect" is a moving journey by Louis Kahn's son to try to understand his father he never really knew through the works he left behind

http://www.pbs.org/flw/

http://www.myarchitectfilm.com/

http://en.wikipedia.org/wiki/Robert_X._Cringely