The Bus Pirate is an inexpensive and insanely useful debugging tool from Dangerous Prototypes. It was first featured on Hack a Day. It allows you to communicate from any PC or Mac to any component that speaks UART, I2C, or SPI. It even has a Logic Analyzer mode, which is not really powerful though. The documentation can be found here.
|Bus Pirate v3||$27.15||$29.95||$30.00|
|Hook with Pigtail||$4.95|
It looks like SparkFun's cable is different, but this is not the case. Always plug the cable in, with the brown up (if the USB is on the right). The pin layout is this: