Loud hen call on the slate or with a diaphram call. They will gobble to that as well. Just make sure you are well hidden before you do it or you will be BUSTED.
Owl in the pre-dawn. After the sun is up good I go with the Crow or a peacock. Turkeys being turkeys, there isn't any 100% fool-proof method to get them to sound off when they don't want to.
I like an owl in the morning also. But sometimes the birds only gobble to a crow in the mornings here in FL. Crow and woodpecker work good in Florida during the day.