I used the following recipe as my favorite brine.  For Butterball turkeys, I cut the salt in half for no particular reason other than my BIL told me to some 15 years ago...but I've used this recipe on Thanksgiving and Christmas turkeys approximately 20 times and, whether frozen/thawed or fresh, it uniformly yields a moist and tender turkey.  As others have said, don't overcook.
I also coat the bird with olive oil and put 1 cutup orange and 4 cutup stalks of celery in the cavity.  Seems to help with adding moisture.  
FWIW, I also like to smoke the turkey in  Smokey Mountain water smoker, but I do the first 1.5 hours without the water pan.
1 gallon water
3 quarts apple juice
3 quarts orange juice
1.5 cups kosher salt
1.5 cups brown sugar
10 cloves
1 tsp nutmeg