ApacheBench HTTP server benchmarking tool & other Apache tools
Did you know that if you are running Apache you already have a HTTP benchmarking tool called ApacheBench aka ab !
Theres a list of all the tools you get with Apache @ http://httpd.apache.org/docs/2.2/programs/ including logresolve which is a post-processing program to resolve IP-addresses in Apache's access logfiles !
Finally there a great list of Open Source performance testing tools @ http://www.opensourcetesting.org/performance.php