I also recommend the already mentioned book City of Darkness and movie Chungking Express. Additional Jackie Pullinger‘s books "Crack In The Wall: Life & Death in Kowloon Walled City" (http://amzn.to/1nNKkuq) and "Chasing the Dragon" (http://amzn.to/1kd9zWc) are worth a read.
One of the best documentaries IMHO is the following 4 part series from 1989 which shows the everyday life in KWC: https://www.youtube.com/watch?v=Lby9P3ms11w
I also recommend the already mentioned book City of Darkness and movie Chungking Express. Additional Jackie Pullinger‘s books "Crack In The Wall: Life & Death in Kowloon Walled City" (http://amzn.to/1nNKkuq) and "Chasing the Dragon" (http://amzn.to/1kd9zWc) are worth a read.