This book applies the same engaging style, entertaining illustrations, and clear approach to describing techniques for usability testing that almost anybody can undertake for their projects. It's particularly helpful if you make your living designing web sites, but are never given time or budget to 'properly' user-test them.
Krug provides straightforward strategies for testing all stages of a design project, from the back of a napkin to wireframe to finished project. Each of the sections provides just enough guidance to get started but not so much that you get bogged down in details. Once you're started, you can go on to get serious with books like Handbook of Usability Testing: Howto Plan, Design, and Conduct Effective Tests