In this video, Salman Khan of Khan Academy explains standard deviation.
Khan Academy

In this video, Salman Khan of Khan Academy explains sample variance.
Khan Academy

In this video, Salman Khan of Khan Academy explains variance of a population.
Khan Academy

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

Gives a brief introduction and overview of the fundamental statistic concepts.
University of South Carolina

Descriptive Statistics topics
Wolfram MathWorld

In this video, Salman Khan of Khan Academy explains the normal distribution.
Khan Academy

In this video, Salman Khan of Khan Academy explains binomial distribution. Part 2 of 4.
Khan Academy

In this video, Salman Khan of Khan Academy explains binomial distribution. Part 1 of 4.
Khan Academy
