It depends. Do not brine a ButterBall or similar brand turkey, because it has already been injected with a salt and spice treated fluid. People will tell you not to brine a frozen bird or one that's been water cooled. But Alton Brown actually defrosts his frozen turkeys by submerging them in a brine, which is good enough for me.
Here's my recipe for a fresh (or defrosted) 14-lb bird:
Make six ice packs by filling quart zip-lock bags with water and freezing over night.
Put 8 pounds of ice and three ice packs in a cooler.
Start brine with 3 quarts filtered water, 2 12-oz. beers, and 1 cup bourbon in a large pan or Dutch oven.
Bring to a boil.
Add 1 cup pickling salt (it dissolves better), 1/2 cup brown sugar, 1 tablespoon garlic powder, and 1 tablespoon onion powder. Stir until dissolved. Remove from heat and allow to cool slightly.
Put the following into a cheesecloth bag: 1 tablespoon whole black peppercorns, 1 bayleaf, 1 sprig rosemary, 1 sprig sage, 3-4 garlic cloves. Add bag and 2 halved lemons to brine. Pour brine into cooler and stir until temperature drops to icy.
Put thoroughly rinsed bird into brine. Make sure it is fully submerged. if not, add additional water into which you have dissolved 4 tablespoons of pickling salt per quart.
Allow to sit overnight. First thing in the morning you need to check temperature of the water. If it's above 40 degrees, add more ice packs. (Don't add ice, which would dilute brine.)
Remove bird from cooler and very thoroughly rinse it. Rinse out cooler and fill with 2 gallons icy water. Return bird to cooler for 30 minutes. Remove, rinse again, drain, and pat thoroughly dry. Do not stuff with stuffing. (Ditto re Alton Brown.) Instead add 1 sliced onion, 1 sliced apple, 1 sliced lemon, a bay leaf, and a few garlic cloves to the cavity.
Preheat the oven to 500 degrees. I start with the bird breast side down in a roasting pan with a rack. After 30 minutes, I flip the bird over and reduce the heat to 350 degrees. After about 90 minutes, I use an instant read meat thermometer to take the bird's temperature. Make sure the probe does not touch the bones. I want the thigh meat to hit 170 degrees. Carryover heat will bump it up 5-10 degrees.
Let turkey rest at least 30 minutes before carving. Do not skip this step.
If you make a pan gravy with the drippings, note that they will be saltier than those from an unbridled bird. Use a low sodium stock and taste carefully before adding any additional salt to the gravy. Note that using Wonder flour to thicken the gravy rather than making a roux is a useful shortcut.
Here's my turkey gear: