I have been using The Grinder to load test a network application I am writing at work. It is easy to set up and does it's job well. It also produces useful statistics that I had been converting to csv and importing into spreadsheets to analyze. Today, I came across
Grinder Analyzer which parses the grinder logs and creates nice looking graphs. Both use Jython which I have a love/hate relationship with. I love the Python scripting side, but hate some of the Java integration (e.g. converting a Jython string to a Java string so I can call getBytes()). Overall I consider both valuable additions to my toolset.