Government Agencies: 
FAA (US) Federal Aviation Administration
access to FAA and other safety databases 
NTSB (US) National Transportation Safety Board
Organization, reports, databases and current releases
ICAO International Civil Aviation Organization
This website lists ICAO news, publications, library, and other current information.

Flight Test and Safety Sites: 
US Navy Flight Test Web Site
US Navy's Flight Test program web site. Description of facilities and programs.
NASA-Dryden
Introduction to NASA flight maneuvers
Edwards Air Force Base
Access to various flight test programs based at EAFB. 
NASA International Safety Lessons Learned
Accessible only to authorized users. 
Society of Experimental Test Pilots
SETP's home page
Society of Flight Test Engineers
SFTE's home page. 
Flight Test Lessons Learned, Gippsland GA-8
Lessons learned during the flight tests of this aircraft, by Sean Roberts. 

Safety and Investigation Sites: 
Flight Safety Foundation Flight Safety Foundation
Organization, publications, and current information
Air Safety Home Page Webmaster Todd Curtis
An aviation safety analyst specializing in air transport accidents
organized by airline type of aircraft, date, type of accident etc.
Aviation Safety Connection
Commercial, but interesting summary of current happenings in aviation safety,
focusing on improved pilot judgment and aeronautical decision making.
  NASA Safety and Risk Management Division
Access to NASA safety and risk management information and resources. 
USAF Safety Center
USAF Safety Center and web links to other aviation safety sites. 
US Navy Safety Center
Links to Naval Aviation safety issues.
US Army Safety Center
Links to Army Aviation safety issues.
Geis-Alvarado & Associates
Aviation safety training and consulting services.

Human Factors Sites:
FAA Human Factors
Human factors database. Location of Advanced CRM Training Manual 
FAA Civil Aeromedical Institute (CAMI)
Information on medical and human factors issues.
ASPECT ONE Human Error and Human Factors
Database of human factor information and case studies. 
NASA Human Factors
The NASA Human Factors Research and Technology Division 

Academic Sites:
National Test Pilot School
Access to NTPS information and programs.

Other Interesting Sites:
Helicopter Association International (HAI)
HAI organization, publications, current information. 
Aviation Week
This is an outstanding research tool. The "Safety Oasis" button leads
to links to a large number of other aviation safety databases
Vermont Safety Information Resources, Inc
MSDS Library.