I am a new member, but just thought I would list some of my favorites. I'm not interested in anything after the early 60's, and my reading reflects that. Some of these have no doubt surfaced here before.

1. Murder, Inc, Feder and Turkus. Not always accurate, but still a classic.
2. I'll Do My Own Damn Killin', Gary Sleeper. Great stuff on the Texas mob and the war between Benny Binion and Herb Noble. A fine book on a very neglected area.
3. Capone, John Kobler. Another oldie but goodie.
4. The Life and Times of Lepke Buchalter, Paul Kavieff. Very dry, well documented, and factual, which I like.
5. The Green Felt Jungle, Ovid Demaris and Ed Reid. Fun and informative. Guaranteed to destroy any romantic sucker illusions about the 'glories' of old Vegas.
6. Barbarians in Our Midst, Virgil Peterson. A classic and very thorough account of the Outfit in its glory days.
7. Washington Confidential, Jack Lait and Lee Mortimer. Pulpy and hysterical, but contains some information about gambling and vice in Washington and Baltimore and the little-known and less written-about outfits that ran the rackets in those places.
8. Tough Jews, Rich Cohen. Often sloppy and embarassingly fanboyish, but it is a fun read in places and contains some things that you can't find in Turkus and Feder.
9. The Murderers, Harry Anslinger. The dope racket as seen by the man who fought it for 30 years.
10. Kill the Dutchman, Paul Sann. Another familiar title, written by an old time reporter who knew the story.
11. and 12. Welcome to the Tiger Inn and Crimetown, USA, Allan R. May. The story of the Youngstown rackets from the 30's to the early 60's, two highly detailed works by an expert on the subject.
13. East Side, West Side, Alan R. Block. Covers the development of the mobs in New York from the late 20's to the early 40's. Heavy on theory in places, but has much precious information about Murder Inc., Mangano-Anastasia on the docks, and Zwillman et al in Jersey.