Igvita's info-packed post (and httperf wrapper code)
http://www.igvita.com/2008/09/30/load-testing-with-log-replay/
Pretty much the Perl equivalent
http://www.xenoclast.org/autobench/
Autobench tutorial
http://agiletesting.blogspot.com/2005/04/http-performance-testing-with-httperf.html
How (not) to abuse stats