"Into The Kill Zone: Cops' Eye View Of Deadly Force," by David Klinger
"Black Mass: True Story of an Unholy Alliance Between the FBI and the Irish Mob," by Dick Lehr and Gerard O'Neill (IMO, it should be required reading for any cop that works with informants, and/or supervises those who do.)
"Lines And Shadows," by Joseph Wambaugh
"Fire Lover," by Joseph Wambaugh
Every non-fiction Wambaugh book I've read has been excellent, but I've tried the fiction, and it's just not good enough to justify the time.
For fiction check out "LA Confidential," by James Ellroy