Also see my – Problem Books for Pure Math, Physics and Mathematical Physics
If you are looking for some of the most important, yet elegant math proofs, look no further than these two books.
The first one – Proofs from the book – The book is dedicated to the mathematician Paul Erdős, who often referred to “The Book” in which God keeps the most elegant proof of each mathematical theorem.
The second one – 100 great problems of Elementary Math – This interesting book covers 100 of the most famous historical problems of elementary mathematics. The book provides insight into the extraordinary ingenuity of some of the greatest mathematical minds of history — Archimedes, Isaac Newton, Leonhard Euler, Augustin Cauchy, Pierre Fermat, Carl Friedrich Gauss, Gaspard Monge, Jakob Steiner, and many others…
If you have any other books or online resources you would like to contribute to this list (book containing elegant proofs only), feel free to comment.