When the big bags of frozen boneless, skinless chicken breasts go on sale, I buy as many as I can. When I get home, I open a bag and throw the whole thing in the slow cooker on low for the rest of the day. After it has cooked at least 6 hours, just pull the chicken apart using two forks or your (clean) fingers.
You can use it in a recipe right away, or let it cool and bag it up into portions you will need for recipes later. The works great for any dish that uses shredded or diced chicken, including Bankok Chicken, Chicken Enchiladas, etc. Add some taco seasoning and a little water and you have a great taco filling. Add barbeque sauce and you're halfway to quick sandwiches.