By convention, Cohen's d of 0.2, 0.5, 0.8 are considered small, medium and large effect sizes respectively.
Cohen's d  

Pearson's correlation r  
Rsquared  
Cohen's f  
Odds ratio (OR)  
Log odds ratio  
Areaundercurve (AUC) *common language effect size statistic


Fisher's z (z') 
All conversions assume equalsamplesize groups.
$$ r = {d \over \sqrt{d^2 + 4}} $$
$$\text{auc} = {\phi { d \over \sqrt{2}}} $$
$$ f = {d \over \ 2} $$
$$ z' = 0.5 * (log(1 + r)  log(1  r)) $$
$$ \text{log odds ratio} = {d \pi \over \sqrt{3}} $$
1. Ruscio, J. (2008). A probabilitybased measure of effect size: Robustness to base rates and other factors. Psychological Methods, 13(1), 1930. doi:10.1037/1082989x.13.1.19
2. Cohen, J. (1988). Statistical power analysis for the behavioral sciences (2nd ed.), Hillsdale, NJ: Erlbaum.
3. SánchezMeca, J., MarínMartínez, F., & ChacónMoscoso, S. (2003). Effectsize indices for dichotomized outcomes in metaanalysis. Psychological Methods, 8(4), 448467.
4. Wikipedia: Fisher's ztransformation of r
5. Borenstein, M., Hedges, L. V., Higgins, J. P. T., & Rothstein, H. R. (2009). Introduction to metaanalysis. Chichester, West Sussex, UK: Wiley.
6. Rosenthal, R. (1994). Parametric measures of effect size. In H. Cooper & L. V. Hedges (Eds.), The Handbook of Research Synthesis. New York, NY: Sage.