This site is a glossary of statistical terms:
http://www.stat.berkeley.edu/users/stark/SticiGui/Text/gloss.htm
This site provides some practice with the mean:
http://www.robertniles.com/stats/mean.shtml
This site provides some practice with the median:
http://www.robertniles.com/stats/median.shtml
This interactive site calculates the mean, median, and mode for a data set.
http://www.calculatorsoup.com/calculators/statistics/mean-median-mode.php
Mean, median, and mode discussion.
http://www.shodor.org/interactivate/discussions/sd1.html