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

A helpful scientific calculator that runs in your web browser window.
Holt Online Learning

This site is designed to provide information, demonstrations, links and quizzes associated with the statistics and statistical methods for research design and analysis. It includes tuorials and applets
WebStat

Online Textbook for a variety of statistical tests
Statistica Website

The website indexes lectures in Introduction to Statistical Methods course.
Lecture Summaries: Introduction to Statistical Methods

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

Explanation of Sum of Squares,Pearson's Correlation Coefficient,Hypothesis Testing,Hypothesis Testing Revisited
Stats:Correlation

Correlation Coefficient definition, and its connection to Least Squares
Wolfram MathWorld

correlation definition
Wolfram MathWorld
