Exploring bivariate numerical data (Khan Academy)
This unit from the Khan Academy starts with scatterplots and correlation before moving on to OLS regression and trend lines.

Advanced regression (Khan Academy)
This unit from the Khan Academy builds on the unit on bivariate regression to look at statistical inference with regression.

Multiple regression (Barnard College)
This tutorial from Barnard College shows how to carry out ordinary least squares regression using more than one independent variable. Once the page is accessed the user must scroll to the ‘multiple regressions’ section.