The energy bill
I expected to call Xcel Energy (a company that provides power to where I'm based in Colorado as well as to North Dakota, South Dakota, Minnesota, Wisconsin, Michigan, New Mexico, and Texas) and hear energy-saving tips to save on your bill every month. And that's what I got: super-helpful tips to reduce my energy bill. But they were also happy to reduce my bill for me.
In exchange for a $40 credit once a year, I enrolled in a program that lets Xcel use fancy air-conditioning technology to "manage my AC use" for short periods of time when demand is super high for electricity in the summer. They only usually need to use this once or twice a season, and it never goes on during the weekends. They say the majority of people never notice when they use it. It helps the company reduce the risk of brownouts and blackouts for everyone, and I get the equivalent of one almost-free energy bill.