Calculus the Easy Way
Douglas Downing
Barron's Educational Series
I came across this book in high school.  In my senior year I had a rather serious case of mono that kept me home for months.  The district sent a "homebound" teacher to keep me current with my classes, but she was not able to help with my AP calculus class.  So, my mom got this book for me and it was very engaging.  I finally understood real-world applications for calculus and understood the reasons behind the formulas.  When it was time for the test, I received a greater score than my classmates.  It took me longer to take the test because I didn't know the formulas from memory as well.  However, I was able to reconstruct them because I had an understanding of the why and how behind the formulas.  Few books have made me smile when I think of them many years later, but I still have a fondness for this one.