Intro to Linear Regression

I'm putting together a class that's more or less an introduction to regression - enough of ordinary least squares (OLS) to be able to understand some empirical results, but not go any further. I wasn't sure what might be a good paper to help, but then Blattman posted a link to this paper, which was written for lawyers, housed at the Chicago Working Paper Series for Law and Economics. I'm on page 8, and it's great.