This is by far my favorite BBQ chicken recipe so far. Here's the exact recipe from allrecipes.com, then I added my own variation.
6 frozen skinless, boneless chicken breast halves
1 (12 ounce) bottle barbeque sauce
1/2 cup Italian salad dressing
1/4 cup brown sugar
2 tablespoons Worcestershire sauce
1. Place chicken in a slow cooker. In a bowl, mix the barbeque sauce, Italian salad dressing, brown sugar, and Worcestershire sauce. Pour over the chicken.
2. Cover, and cook 3 to 4 hours on High or 6 to 8 hours on Low.
Here's my variation:
First, I put the chicken in the slow cooker frozen and let it cook for four hours in 2-3 cups of chicken broth. This makes the chicken super tender and juicy.
Then drain the chicken broth, shred the chicken, and add the BBQ sauce mix. Cook for another 2 hours on low.