I've made buttermilk panna cotta before, to spectacular results. This incorporates homemade yogurt (Greek or plain yogurt would work just as well) for a tangier, slightly thicker panna cotta.
1 envelope unflavored gelatin (2 1/4 teaspoons)
2 tablespoons cold water
1 cup heavy cream
1/3 cup sugar
1 vanilla bean, split, seeds scraped
One 17.6-ounce tub of Greek yogurt (2 cups)
In a small bowl, sprinkle the gelatin over the cold water; let stand until softened, 5 minutes. In a small saucepan, bring the cream, sugar and vanilla bean and seeds to a simmer. Off the heat, stir in the gelatin until melted. In a bowl, whisk the yogurt until smooth. Gradually whisk in the vanilla cream; remove the vanilla bean. Pour the mixture into six 1/2-cup ramekins and refrigerate until set, at least 3 hours.