The SparkFun Joystick Shield Kit contains all the parts you need to enable your Arduino with a joystick! The shield sits on top of your Arduino and turns it into a simple controller. Five momentary push buttons (4+ joystick select button) and a two-axis thumb joystick gives your Arduino functionality on the level of old Nintendo controllers. Soldering is required, but it's relatively easy and requires minimal tools.
The momentary push buttons are connected to Arduino digital pins 2-6; when pressed they will pull the pin low (utilizing the internal pull-ups of the Arduino). Vertical movement of the joystick will produce a proportional analog voltage on analog pin 0, likewise, horizontal movement of the joystick can be tracked on analog pin 1.