Currently I'm reading Roemer: Man Against the Mob. Bill Roemer Jr. was an FBI agent working out of the Chicago office. One of his greatest accomplishments was being the first to put a microphone in the mob headquarters. (they called it "Little Al")

This is his first book, but the last of his I'm reading. I actaully really like his books. They're very informative.

I highly recommend his books as well.
The Enforcer: The Chicago Mob's Man Over Las Vegas
Accardo: The Genuine Godfather
War of the Godfathers

Of all his books War of the Godfathers seems more like fiction to me.