Place chili beans, black beans, corn, tomato sauce, beer or broth, diced tomatoes and onions in a 6 quart slow cooker. Add taco seasoning, and stir to combine. Lay chicken breasts on top of the mixture, pressing down slightly until covered by the other ingredients.
Cover and cook on LOW for 6-8 hours.
A half an hour before serving, remove the chicken and shred. Stir shredded chicken back into the soup.
Serve soup topped with crushed tortilla chips, shredded Cheddar cheese, a dollop of sour cream, and fresh chopped cilantro.