OWASP Resources - Open Web Application Security Project
The Open Web Application Security Project is an online community that produces freely-available articles, methodologies, documentation, tools, and technologies in the field of web application security. The OWASP Testing Projects have been in development for many years. The aim of the project is to help people everyone interested in Web Security to understand the what, why, when, where, and how of testing web applications. If you are getting started with Web Application Security Testing, here's are few OWASP resources that will help you get ahead in Web Security.
Good Luck and Happy Hacking!
You may also be interested in reading, Web Security for Anybody and a Step by Step Guide on a How to Create Your First Ethical Hacking Environment.
What other sites have you used to practice on? Let us know below!