1.The Development of the Digital Computer
2. Gôdel's Incompleteness Proof
3. Einstein's Relativity Theory
4. Proof of Fermat's Last Theorem (Wiles)
5. Hilbert's Talk at the 1900 Congress
6. Classification of Finite Simple Groups
7. Development of Linear Programming (Dantzig)
8. Mathematization of Quantum Mechanics (Von Neumann)
9. The Development of Fractal Geometry (Mandelbrot)
10. Applications of Mathematics to Cryptology.
The results of the Michigan Section's Top Ten vote can also be found online, at http://www.cst.cmich.edu/units/mth/ttm2k/topten.htm. Perhaps other MAA sections will want to produce their own lists!