Correlation (Pearson r): http://cognitron.umd.edu/power_slates/correlation/index.html
t-tests (independent and dependent): http://www.graphpad.com/quickcales/ttest1.cfm
Chi-Square Goodness of Fit Test: http://cognitron.umd.edu/power_slates/chi_square_prop/index.html
Chi-Square Test for Independence: http://cognitron.umd.edu/power_slates/chi_square_cont/index.html