This site gives a definition and an example of scatterplots. Topics include positive and negative association.
The fifth chapter of an online Introduction to Biostatistics course. Three sets of lecture notes are provided. Additionally, links for additional reading and exercises with solutions are provided. A link is also given for a related statistical applet on the normal distribution.
This page will calculate the intercorrelations (r and r2) for up to five variables, designated as A, B, C, D, and E.