The Grinder
Distributed load testing framework - Java, Jython, or Clojure scripts.
The Grinder is a load testing framework that makes it easy to run a distributed test using many load injector machines. Test scripts are written in Jython, and can call out to arbitrary Java code, providing support for testing a large range of network protocols.
The Grinder comes with a mature plug-in for testing HTTP services, HTTP scripts can be recorded easily from a browser session.