Statistics at Square One
An introduction to statistics with easy-to-understand explanations written by T. D. V. Swinscow and revised by M. J. Campbell of the University of South Hampton

Instructional Demos in Statistics
A whole series of demonstrations to illustrate and explain various statistical concepts and procedures by HyperStat Online.

Statistical Analysis Tools and Tables
All tools are free to download - from HyperStat Online

Statistical Tables and Formulas from math.com