If you want to use a computer to send commands to the arduino then use Processing (arduino's computer based cousin). There is a library included in the software package that allows you to interface with the arduino though the usb serial connection.
If you want to control the whole setup remotely, you can use an xbee shield and radio to create a wireless serial connection between two arduinos.
Personally, I have used ps2 controllers as shown in this link (
http://www.billporter.info/playstati...-library-v1-0/). It's much cleaner than soldering the connections to the potentiometers inside the controller, plus you can do some interesting things with the ruble feature, etc. There is also some canned code on that web page.
The web site also has a library for creating complex serial communication protocols (which comes in handy when you want to transmit more than one variable over a serial connection).
PM me and I can send you pictures of the project setup and code (if I can find it).