FS2Crew develops advanced Airline Flight Crew Simulations and other quality Flight Simulator add-on products for Microsoft Flight Simulator X, Prepar 3D, Microsoft FS9/ FS2004 and Steam FSX.
SimBrief's Integrated Dispatch System is the web's most detailed FREE virtual flight planning service. Features include accurate fuel planning for over 100 aircraft types, real world weather forecasts, current NOTAMs, ETOPS planning, several real world airline OFP layouts, and much more.
iniBuilds provides us with up-to-date liveries via their iniVA service, an essential fleet management service. They also have plenty of other amazing downloads and products on their website, so do check them out!
VATSIM is the Virtual Air Traffic Simulation network, connecting people from around the world flying online or acting as virtual Air Traffic Controllers. This completely free network allows aviation enthusiasts the ultimate as-real-as-it-gets experience.