I just released a new open source tool for performance testing Web Services.
If you are interested, visit: www.pylot.org
Pylot is a free open source tool for testing the performance and scalability of web services. It runs HTTP load tests, which are useful for capacity planning, benchmarking, analysis, and system tuning. Pylot generates concurrent load (HTTP Requests), verifies server responses, and produces reports with metrics. Tests suites are executed and monitored from a GUI.