I have done a pretty extensive search for crime rates (violent and/or property) by zip code that I can use to create a crime heat map. I would even take the number of crimes by type by zip code so that I could infer my own crime rate. But I haven't been able to locate a national data source.
The FBI tracks crime rates nationally. It is a voluntary (by local law enforcement departments) systems, so accuracy varies. Also note: these are citizen-on-citizen crimes, and do not include police-on-citizen crimes (murders). Here's the link: