They're both among my fave books of all time, though they are relatively similar in content so getting just one is fine.
They cover a lot of different strategies for thinking creatively and outside the box, provide tons of examples, and have a lot of exercise that you can try yourself (and while it sounds cheesy, the exercises are actually fun)
Thinkertoys (http://www.amazon.com/Thinkertoys-Handbook-Creative-Thinking...)
Cracking Creativity (http://www.amazon.com/Cracking-Creativity-Secrets-Creative-G...)They're both among my fave books of all time, though they are relatively similar in content so getting just one is fine.
They cover a lot of different strategies for thinking creatively and outside the box, provide tons of examples, and have a lot of exercise that you can try yourself (and while it sounds cheesy, the exercises are actually fun)