Don Norman's book The Design of Everyday Things has indeed altered how I look at the world from a design perspective. It teaches you design awareness, and you'll find yourself noticing and understanding design elements all around you, that you didn't before. Even though it might seem a little old, the information presented in there is timeless, so I highly recommend it as well. It is in fact the first book I would suggest to anyone wanting to learn how to think like a designer.

I recently got his other book, Emotional Design, I just haven't gotten to it yet.