Bill Brandt, Cartier-Bresson, Avedon's early Paris work, James Wong Howe, Lillian Bassman, Paolo Roversi, Daido Moriyama.
I just saw a movie yesterday that gave me an idea I'm excited about. Good web sites that cross genres are great. I was looking at a photography video and came across an interview of Edward Hopper on this one site and that led me to see a connection between his work and where I was going with my color street work.
Keeping fresh is sometimes a challenge. I basically switch the type of work I do and my tools that go with a particular type of work if I'm feeling a bit bored or find myself at a dead end.