iBeta is the first website I found. iBeta offers website testing services and will systematically test every aspect of your website's technology including applications, client-server systems, eCommerce platforms and more.
UsabilityGeek is the second site I found. It defines usability as how easy an object is to use. The object can be almost anything, including a machine, tool, process, book, software application or website. Anything that a person can interact with should be usable. In the case of websites and software applications, usability has been defined as the ease at which an average person can use the software or website to achieve specific goals.