Get an X-Box 360 controller for PC. I put off doing this for a long, long time because I preferred to use the keyboard, but after they started making almost all games require that you control the camera in addition to movement rather than being the same keys, I finally broke down. It's made things so much easier, even car racing. You would not believe.
The reason I say to get a 360 is that other controllers seem more fragile. I went through a whole mess of them before going 360, and even then I only did because it was the only one available at the time. That was 2 years ago, and I haven't replaced my controller since. There has been damage from wear and tear, but zero damage from dropping. They come wireless, now, too.
Oh, and to answer your question: It's the A button, the same as the jump button.