This tools listing has been loosely organized into the following categories: 
Load and Performance Test Tools 
Java Test Tools 
Link Checkers 
HTML Validators 
Free On-the-Web HTML Validators and Link Checkers 
PERL and C Programs for Validating and Checking 
Web Functional/Regression Test Tools 
Web Site Security Test Tools 
External Site Monitoring Services 
Web Site Management Tools 
Log Analysis Tools 
Other Web Test Tools 

(Categories are not well-defined and some tools could have been listed in several categories. Note that the 'Web Site Management Tools' category includes products that contain: site version control tools, combined utilities/tools, server management and optimization tools, and authoring/publishing/deployment tools that include significant site management or testing capabilities. Suggestions for category improvement are welcome; see bottom of this page to send suggestions.)