Once you've designed something, these books cover how to find out if it's well designed.
Rocket Surgery Made Easy: The Do-It-Yourself Guide to Finding and Fixing Usability Problems
A companion book to Steve's Don't Make Me Think. This book is a practical guide to usability testing on a small money and time budget. If you need to find out whether people can use your design, no matter what stage it's at, this is the book for you.
Universal Methods of Design: 125 Ways to Research Complex Problems, Develop Innovate Ideas, and Design Effective Solutions
This book has already been mentioned in the user research section, but it also lists usability evaluation methods. Each method is given a two page spread, so you can quickly learn how to carry out methods.