Regents Prep - Put out by the NY Board of Regents; excellent explanations, examples, and practice problems. Has resources for both Algebra and Geometry.

NCTM Line of Best Fit - Application that allows you to create a scatter plot, estimate a line of best fit, and compare with a computer generated line of best fit.

Mathbits Line of Best Fit - Example of how to find a line of best fit using the paper and pencil method, and with the graphing calculator.