Site has a program where you can input data values and it will calculate the mean, standard deviation, or plot data on a histogram.
WebMath

You can search this electronic textbook for statistics topics including ANOVA, linear regression models, the effects of outliers, confidence intervals, etc. Gives explanations and discusses the topics.
StatSoft

This website provides graphical displays, an index of online calculators and summaries of main topis in statistics.
Statistics to Use

Goes over collecting and organizing data into frequency tables, histograms, box and whisker plots, and stemandleaf plots. Also shows finding mean, median and mode. Many include videos!
Online Math Learning

Definition of Quartiles, Five number summary, and Boxplot
Percentiles
zscores
Quartiles, boxplots, percentiles, and zscores

It also gives formulas, description, etc for statistics.
Wolfram Mathworld

Page with links to several resources about finding mean, median and mode, plots and graphs used in statistics and the general process of collecting data for statistic studies.
Statistics Canada

Central Limit Theorem Tutorial
Intro to the Central Limit Theorem Tutorial

Interactive applet that allows a student to plot points on a graph and see how an outlier affects the regression line of the data points.
Illuminations NCTM

Statistics: Power from Data! is a product from Statistics Canada that will assist readers in getting the most from statistics. Each chapter is intended to be complete in itself, allowing users to go directly to the topic they wish to learn more about without reading all of the previous sections.
Statistics: Power from Data!
