Differential Equations with Applications and Historical Notes, George F. Simmons, McGraw-Hill, 1972.

I acquired this from Amazon based on a recommendation from Steven Strogatz's (@stevenstrogatz) twitter feed on January 9.  Strogatz commented: My favorite preface to a math book is that written by George Simmons in "Differential Equations with Applications and Historical Notes." He then went to on to quote part of the preface.  It was so attractive that I had to see the book, so I ordered a copy.  I got a first edition copy, there are also second and third editions.  The book is well suited to physic and engineering students.  I could say more, but check it out in your library - it is well worth your time.