AVSIM Online - Flight Simulation, Flightsim, flight sim, flight simulator, fsx, fs10
FlightSim.Com - World's #1 Flight Simulator Site For Downloads, Files, News, Reviews, Add-ons
Simviation Freeware Addons for PC Flight Simulator Programs. Flight Simulator X, FS2004 - Tens of Thousands of free high quality add-ons for Microsoft's Flight Simulator series and other PC Flight Simulators! Quality Freeware Add-ons and support!
those websites have tons of addons for Flightsim 2004 and the latest flightsim X. All of them free
The FlightSim Store: Your Source for Flight Simulation Software and Accessories
Those guys have payware aircraft, generally alot more realistic than the free stuff
If you need a hand adding the aircraft to the flight sim just ask mate