Handbook of Usability Testing: Howto Plan, Design, and Conduct Effective Tests

This book is absolutely perfect. I received my copy of it last night and stayed most of the night reading through it as I simply couldn't put it down. I've been working as an interaction designer / usability tester for a couple of years and this has overnight become my new favourite reference book. It's easy to read without glossing over essential detail (a criticism I have of many modern usability books). This book is filled with practical advice on how to communicate data, manage integrity and measure the user experience in a business setting.
I followed the recommendations and researched a method to cheaply run user tests and decided on userfly(.com). It allowed me to view videos of my users interacting with my site!!