This page from the FBI breaks down crime statistics by year as well as by certain types of crime (terrorist activities, fraud, etc.).

This FBI report gives information on violent crimes related to gang activity.

This site records arrests, burglaries, attacks, and other crimes onto an interactive map.

This site collects data from reported crimes.

Currently centered on San Francisco, this site allows users to search a location based on several criteria. Use the "Crime" tab at the top of the map and enter in the location you wish to search.