Pizza Boy is right - he should definitely check out 5 Families. It's about New York only, but in spite of what fanboys of other families say New York is and always has been the ceneter of the majority of mob activity(even back when all 25 or so families were flourishing, including the Outfit, probably at least more than 50% of Italian-American mob activity was concentrated in New York and its immediate surroundings, like east New Jersey - and today it's probably 95%), and you should get a good grounding in them if you want to understand the mafia in any meaningful way.

Yeah, read Five Families after The Idiot's Guide to the Mafia, but before the other stuff.

I also recommend watching Goodfellas and Casino if you haven't already, though bear in mind that the mob is "prettied up" a bit in those. (Henry Hill is a grotesque little lizard man in real life - certainly not a Ray Liotta type guy).

And if you're really hard core, check out The Origins of Organized Crime in America for a thorough rundown of pretty much everything that is known about the origins of the mob. It's also essential because it dismantles a lot of myths in the standard mob historiography.

As for Pistone's books: Donnie Brasco is pretty good, but the rest I got the feeling that Pistone cranked them out because he wanted to buy a new boat or something. Didn't he also write some retarded "new adventures of Donnie Brasco" novel or something?