An Introduction to Statistical Learning with Applications in R, Gareth James, Daniela Witten, Trevor Hastie, Robert Tibshirani, 2013 (Springer) - Chapter 3 discusses linear regression, including detailed explanations of MSE, RMSE, and R-squared for model evaluation.
CS229 Lecture Notes: Linear Regression, Andrew Ng, 2004 - Lecture notes from a renowned machine learning course, providing a clear and concise explanation of linear regression and its evaluation metrics like MSE.