A simple-to-use program for computing power analyses for all common test statistics (and beyond). For details click here.
For more details see:
Faul, F., Erdfelder, E., Lang, A. G., & Buchner, A. (2007). G*Power 3: A flexible statistical power analysis program for the social, behavioral, and biomedical sciences. Behavior Research Methods, 39, 175-191.