If you've ever used JMeter, you know it's an awesome load testing tool. It also comes with a built-in graph listener, which allows you to watch JMeter do, well... something.
While this gives a basic view of response time and throughput, it doesn't show failures, nor how the server responds as load increases. And let's face it, it's just plain ugly.
Enter Matplotlib, a beautiful (though complex) plotting tool written in Python.