The millenium seemed to spur a lot of people to compile "Top 100" or "Best 100" lists of many things, including movies (by the American Film Institute) and books (by the Modern Library). Mathematicians were not immune, and at a mathematics conference in July, 1999, Paul and Jack Abad presented their list of "The Hundred Greatest Theorems." Their ranking is based on the following criteria: "the place the theorem holds in the literature, the quality of the proof, and the unexpectedness of the result."
J. Thaler, and K. Van Tilburg. (2011)cite arxiv:1108.2701Comment: 32 pages, 15 figures, 3 tables; v2: references added, small clarifications, additional figure.
D. Romero, B. Meeder, and J. Kleinberg. Proceedings of the 20th international conference on World wide web, page 695--704. New York, NY, USA, ACM, (2011)
U. Langenfeld, S. Moch, and P. Uwer. (2009)cite arxiv:0907.2527
Comment: 5 pages, 9 figures, to appear in the proceedings of the XVII
International Workshop on Deep-Inelastic Scattering and Related Subjects, DIS
2009, 26-30 April 2009, Madrid.
D. Howard. Proceedings of the 8th International Conference on
Knowledge-Based Intelligent Information and Engineering
Systems Conference, KES 2004, Part III, volume 3215 of Lecture Notes in Artificial Intelligence, page 217--223. Springer, (September 2004)