I need to express my love for OWASP’s Live CD (aka OWASP Web Testing Environment). Its backtrack-like philosophy of piling in the web-security tools is simple, but the end result is a wonderful testing environment. Firefox comes action-packed with web testing addons, a pile of proxies (burp, paros, rat), a multitude of scanners (grendel,w3af), and an array of other tools.
While the forums and tutorials on the site are a bit slim at the moment, its a great start to a growing resource.
Get the iso’s and VM images here: http://appseclive.org/