Not quite a mafia book but includes it.
I'd like to recommend King of the Mountain by Billy J Chandler. It is the most unbiased view i've ever read on Salvatore Giuliano. One of my main favourite parts of it is the detail in which it goes into the disaster at the Porta Della Ginestra.
It's quite a very political read, goes into Giulianos views and his fight for Sicily to become the 49th state.