Here's a step-by-step process to barbequed chicken nirvana. It looks like a lot of work, but it's really not. Let's dive right in. Click the images for larger versions.
1 whole chicken (4-6 lbs)
5 cups (approximate) of your favorite marinade. Of course, I recommend mine.
1/3 cup of your favorite BBQ seasoning
Start with a large clean cutting board. Remove your chicken from its bag. Pull the neck and innards from the cavity and rinse well (inside and out) with cold water. Shake off the excess water and set the chicken on a double layer of paper towels on the cutting board.
Turn the chicken over so that the back is facing you. Cut completely through the rib cage about 1/2" on either side of the backbone. This is where kitchen shears are highly recommended. Be very careful if you are using a knife. Discard the backbone, or keep it to make broth or stock.
Push the two halves of the chicken apart to expose the breast (keel) bone. Slide your index finger under the bony part of the keel and pull toward you. If the bony part separates from the cartilage portion (which is likely), just cut gently along either side of the cartilage and coax it out.
Use the knife to completely separate the two halves. Rinse each half and pat dry. If you skip the cutting part and just flip the bird over and flatten it, you'll have a nicely butterflied chicken. I prefer to separate the halves because it's easier to handle when cooking. You'll have to separate them when carving anyway.
Put each chicken half in a gallon zip-top bag. Add 2 1/2 cups of the marinade to each bag (or enough to fully cover the chicken). Seal each bag while removing the excess air. Put the bags in a baking dish and marinate in the refrigerator 2-4 hours. If you are using a store-bought marinade, follow the directions.
Remove the chicken from the marinade and shake off the excess. Starting skin side down, season each side liberally and evenly with the BBQ seasoning. This may seem unnecessary given the marinating, but this adds another layer of flavor and will help give us that lovely colorful skin.
Start your fire, or light your gas grill and prepare for indirect cooking at medium-high heat. Of course, this won't really be barbeque without some smoke flavor, and I recommend cherry chunks or chips for poultry. Cook at 300-325º until the thighs reach 165º (about 2 1/2 hours), turning once halfway through.
Remove the chicken from the grill/smoker, tent with foil and let rest about 10 minutes. If you're really hungry, plate an entire half, roll up your sleeves and get to work. If not, the breast/wing portion will separate almost effortlessly to make four portions. Sit down and enjoy!