I have little personal experience with it, but some colleagues and friends hold the following text in high regard:
Robert M. Young, Excursions in calculus.
An interplay of the continuous and the discrete. The Dolciani Mathematical Expositions, 13. Mathematical Association of America, Washington, DC, 1992.
And here is a very favorable MathSciNet review by F.J. Papp.
This book does not belong on the office shelf of every mathematics instructor, nor does it belong on the book shelves of our students, neither does it belong on our library shelves. Rather, this book belongs on the desk right next to one's current course texts (and not just the calculus texts); as far as the library is concerned, ideally, this title should be nearly always checked out and in constant use. The book is one of those rare works that one can read from cover to cover with great pleasure and profit, or one can simply open to a randomly selected page and begin reading. Anyone with the least interest in mathematics will find something interesting and intriguing on just about every page and will in all likelihood not be able to stop with just one page. The "underlying theme is the elegant interplay that exists between the two main currents of mathematics, the continuous and the discrete''. In the preface, the author rather modestly speaks of his book as one possible supplement to a more traditional calculus course. It is that, of course, but it is also much more than that. It will also serve the very crucial purpose of educating our students and will help them understand that mathematics is not merely a collection of nonoverlapping, unrelated subdisciplines. Rather, they will experience their coursework in a new and much healthier way as, with the aid of this book, they begin to comprehend the essential unity of mathematics and the remarkably synergistic ways in which seemingly unrelated areas of mathematics can interact. Helping one's students to decompartmentalize their understanding of mathematics is in itself worth the price of the book.
Each of the six chapters is divided into several subsections, all but one of which concludes with a number of interesting problems. The subsection titles, included below, will give a tantalizing hint of the fascinating variety of topics to be found in this book. Contents: 1. Infinite ascent, infinite descent: the principle of mathematical induction (Patterns/Proof by induction/Applications/Infinite descent); 2. Patterns, polynomials, and primes: three applications of the binomial theorem (Disorder among the primes/Summing powers of the integers/Two theorems of Fermat, the "little'' and the "great''); 3. Fibonacci numbers: function and form (Elementary properties/The golden ratio/Generating functions/Iterated functions: From order to chaos); 4. On the average (The theorem of the means/The law of errors/Variations on a theme); 5. Approximation: from pi to the prime number theorem ("Luck runs in circles''/On the probability integral/Polynomial approximation and the Dirac delta function/Euler's proof of the infinitude of the primes/The prime number theorem); 6. Infinite sums: a potpourri (Geometry and the geometric series/ Summing the reciprocals of the squares/The pentagonal number theorem); Appendix: The congruence notation. Also included is a very extensive set of 463 references to books and articles. The final two parts of the book are a "sources for solutions'' section and the index. The sources section gives a problem-by-problem cross reference to one or more of the items in the list of references or else indicates that the problem is (at present) unsolved. The book also contains eight color plates (mostly dealing with fractals), numerous additional figures, and a variety of tables. The one section not having a set of problems is the final section of Chapter 6. This section is essentially Pólya's translation from the French of Euler's memoir on his "pentagonal number theorem''—thus giving readers the opportunity, as Abel put it, to "study [one of] the masters''.
Any book published in the Dolciani Mathematical Expositions series will naturally be measured against the remarkably high standards already well established by the previously published titles. In the present case, however, it is safe to say that this latest addition (the thirteenth in the series) not only easily meets the previously set standards but sets an entirely new standard for future volumes.