Here's the recipe my husband used to smoke our first turkey:
1 cup kosher salt
1 cup brown sugar
1/2 cup maple syrup
2 quarts apple juice (or cider)
1 or 2 quarts water mixed with ice (Use enough to allow the turkey to be fully submerged in the brine)
Mix the brine well. Soak the turkey in the brine for at least 16 hours in a cooler.
Pull the bird out of the brine. Rinse off with water, and smoke it until it's 180F.