Tools for load testing

Hewlett-Packard (Mercury Interactive) – HP Performance Center (includes HP LoadRunner)
IBM – Rational Rational Performance Tester
Borland (Segue) – SilkPerformer
AutomatedQA Corp – TestComplete
Microsoft – MS Web Application Stress Tool

A separate item select free tools for automated load testing:

Jmeter – an Apache Jakarta project that can be used as a load testing tool for analyzing and measuring the performance of a variety of services
Grinder – 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 HTTP scripts can be recorded easily from a browser session.