For patrol: Verbal Judo by George Thompson is very good. The 3 Calibre Press books are excellent. Total Survival by Ed Nowicki et al covers a lot of topics. Emotional Survival for Law Enforcement by Kevin Gilmartin will help you keep a reasonable attitude throughout your career.
I also read Police Magazine, Police Marksman and American Police Beat to keep up to date on a lot of issues. Police Marksman also has a great book with the best of their articles from the last few years.
Policeone.com has a good e-newsletter as does Calibre Press and the Mass. Trial Courts has an e-newsletter with the most up-to-date Mass. SJC decisions available.
For a great combination of info and anecdotes, my personal favorite is "Surviving Street Patrol" by Steve Albrecht. One of the few Paladin Press books that's not geared toward the armchair and/or nutcase crowd.