Taste testing.

Tacit and Explicit Knowledge - written by Harry Collins. I gave this book a try after reading post after post from the likes of Michael Bolton (the tester) lavishing praise upon it. A nice deep, and easy to follow look at knowledge itself.

The Design of Everyday Things - One of my favorite books. The author, Don Norman gives you an eye-opening peek into his vast understanding of the design process. I'll never look at another door in the same way again :)