All-purpose Beschamel Cheese Sauce

Anticipating some belt-tightening, I got into a conversation with a friend about eating cheaply but satisfyingly. He told me that, when he was in college, he had his suitemates pay him a weekly allowance and he would go grocery shopping and have hot meals for them every day. I asked him for some recipes that he used back then, and he sent me an email entitled "The Roux and You" which included this recipe. It's been my first real foray into cheese-based sauces, and I've pretty much perfected it through repetition.