For aviation accident/incident databases, see the Aviation Safety Information Analysis and Sharing (ASIAS) System (formerly the National Aviation Safety Data Analysis Center): http://www.asias.faa.gov
[Note: Temporary session cookies are used to search these databases, so you'll need to click on an agreement button in order to proceed.]
The Federal Aviation Administration (FAA) web site on aviation safety may also be of interest: http://www.faa.gov/safety