Depends on budget and goals:
* If you want to fly something realistic like a Cessna etc, get a yoke. Saitek offers a good combo Yoke/Throttle Quadrant/Rudders, which are a great way to start a fun yet relatively realistic experience. You can then upgrade it with instrument panels etc, but that is if you get quite serious about things. The basic combo is MORE than enough for a long time.
https://www.saitek.com/uk/prod-bak/yoke.html https://www.saitek.com/uk/prod-bak/pedals.html
Alternatively, CH has an "All in one" yoke with hand-controlled rudder and attached throttle. Slightly less realistic (as the rudder is not via feet), more space-saving & compact :)
http://www.chproducts.com/Flight-Sim-Yoke-v13-d-705.html
* If you are not looking for realism of that kind, or want something good value, and/or might fly fighter flight games as well, the Thrustmaster 1600 combo (joystick + throttle) are a reasonable "solid entry" pack.
http://www.thrustmaster.com/products/t16000m-fcs-hotas
* Finally, if you are really on a budget, OR play in living/family room on a couch but don't want to fly with gamepad, Thrustmaster HOTAS/Ace allows you to physically connect throttle and joystick, so you can hold it on your lap or similar and play from anywhere :)
These come in PC+PS4 or PC+XBOX versions:
http://www.thrustmaster.com/en_UK/products/t-flight-hotas-on...
http://www.thrustmaster.com/en_UK/products/t-flight-hotas-4-...
* Note also, TrackIR adds a huge amount of reality and fun, if you don't go the full VR route. It LOOKS like it'd be gimmicky, but once you put it on, it's quite natural and huge amount of fun. I was honestly giggling first time I've put it on and looked to the side and below my plane just by moving my head around :)