Fisher's exact test

Fisher's exact test is described at
http://en.wikipedia.org/wiki/Fisher's_exact_test
with references

Fisher, R. A. (1922). "On the interpretation of χ2 from contingency tables, and the calculation of P". Journal of the Royal Statistical Society 85 (1): 87–94. JSTOR: 2340521.
Fisher, R. A. 1954 Statistical Methods for Research Workers. Oliver and Boyd.
^ Mehta, Cyrus R; Patel, Nitin R; Tsiatis, Anastasios A (1984), "Exact significance testing to establish treatment equivalence with ordered categorical data", Biometrics 40: 819–825, doi:10.2307/2530927, http://www.jstor.org/stable/2530927
^ Mehta, C. R. 1995. SPSS 6.1 Exact test for Windows. Englewood Cliffs, NJ: Prentice Hall.
^ mathworld.wolfram.com Page giving the formula for the general form of Fisher's exact test for m x n contingency tables

Andrew Gelman wrote a blog about it and introduces some of his work,
http://www.stat.columbia.edu/~cook/movabletype/archives/2009/05/i_hate_the_so-c.html