One of the top simulators on the market. Simulates commercial, general aviation, combat, helicopters, and even the space shuttle.
Here you will find a wide range of community created scenery, aircraft, liveries, and plug-ins.
Quality freeware airports and textures.
PROP STRIKE STUDIO
Offers gorgeous hand painted bush flying scenery and a free C172 + taildragger
retrofitted for bush flight.
A brilliant plug-in that makes push back from the gate easy and accurate.
Updates the default textures around airports. Adds more refined painted lines and signs.
Adds more control over the camera allowing you save views and create your own presets.
Adds a runway advisory system to the simulator.
Adds real time weather data to the sim.
ZIBO MOD 737-800X
Arguably the best rendition of a 737-800 out there. The best part is that it's free, although I highy suggest donating to this project because you will fall in love if you're a fan of the 738.