Search for Notices to Airmen (NOTAMs)
FAA's Notam Home Page
UK NATS Aeronautical Information
Search for Airworthiness Directives, NPRM's, etc.
Airworthiness Directives, NPRM's, etc.: Use the above two links to access a search form at the Governement Printing Office servers. There you will find Airworthiness Directives, NPRM's, etc. (Hint: Start with the Federal Register database).
Airline Operators: Contains information pertaining to scheduled airline certification (Part 135 operators), operations, and aircraft counts by make and model.
Air Carrier Fleets Stats: Contains information on air carrier fleets such as aircraft models, monthly flight hours, and engine shutdowns.