Betterrecipes.com offered up this quick and easy crock pot recipe.

4 skinless boneless chicken breast halves  
1 package reduced-sodium taco seasoning mix  
1 cup salsa  
2 tablespoons cornstarch  
1/4 cup light sour cream

Spray the crock pot with cooking spray. Add the chicken breasts. Sprinkle with Taco Seasoning. Top with salsa. Cook on low for 6-8 hours. When ready to serve, remove the chicken from the pot. Place about 2 T cornstarch in a small amount of water. Stir well. Stir the cornstarch mixture into salsa sauce. Stir in 1/4 cup of sour cream. Serve the thickened sauce over the chicken.