Low Life/Poverty

What are some good books that deal with poverty or the seedier side of living? I already know the obvious "Down and Out in Paris and London" by Orwell and "Last Exit to Brooklyn" by Selby (and I'm probably forgetting other obvious entries by they aren't coming to mind right now).

Because I don't feel like this deserves another thread, any good books about drug addicts would also be greatly appreciated. Outside of what has been mentioned in this thread.