You need a lot of differnt components to get a cockpit up and running. Today we can get all sorts of USB devices which can act as analog to digital interface. The most important thing is that your software eg. Prosim needs to support those. Generally Prosim support the most interfaces and is quite easy to configure.
BU0836X from Leo Bodnar was my first interface card. It works as a joystick interface with 32 buttons, 8 axis and a POV hat input. You can connect nearly all switches and inputs to this card.
FlightSimPM delivers a great throttle made in plastic. This was my first throttle and worked great for long time.
CockpitForYou delivers a great throttle made in metal. You can get throttle in differnt versions mine is a V3 Silver and are very detailed and solid.
OpenCockpits delivers a wide sortiment for cockpits builders. They where some of the early ones in our hobby and are delivering a very high quality. Their panels are some of the best in the market, very detailed and with 3 layers so the light are being correct displayed.
Pololu delivers a great Servo interface card which are plug and play with Prosim. Just connect it, add power and go to the Gauges tab in Prosim and configure your servos.
Polabs makes some very great interface cards. The most used is Poeky56U which connect direct to Prosim. Just connect your switch/Encoder/button and select it in Prosim. Each card has it's own serial number you can select the card by this number in Prosim. If you are planning to use many of these cards I would recommend going for the Ethernet version. On my setup 6 Pokeys USB was the maksimum one computer could handle !
FlightSimparts deliverys both Pokeys and some addon cards to this. The Led Extension card make it possible to connect 24 LEDs to a Pokey card. Easy wiring and commom use of power and no need for additional resistors.
FlightSimParts also deliver 7 segments displays and ready to use Electric Panel for the overhead.
The 7 segments display card can be used for Cabin Alt and Lading Alt. You also needs two pcs for the Electrical panel in the overhead.
OpenCockpits also has a LED Output card. It's quite easy to use, but requires a resistor for each LED. I have tried to use two cards at the same time, but no success.
OpenCockpits has also "plug and play" devices like radios etc. They are not quite "plug and play" but needs SIOC and some scripts. These are done and can be used with Prosim, but you still need to have/get some knowledge about configuration of SIOC