Many people have a favourite chilli recipe. To change things up and add some more flavour, try using balsamic vinegar.
Photo by M Glasgow
Balsamic vinegar improves tomato recipes like barbecue sauce, so adding it to chilli isn't that much of a stretch.
The Kitchn suggests adding it at the end of a recipe so you'll really taste the tang. Don't limit yourself to balsamic, either -- any flavored vinegar works here too.