Überfall (1928)
came across this great experimental short banned by German censor in 1928 because of its "brutalizing and emoralizing effect" http://www.imdb.com/title/tt0019616/
also, it's on the public domain, watch it here: http://www.youtube.com/watch?v=4VkcNyRcWRI
i think it's a great start to get into experimental movies