Dark Chocolate Fondue: swap the 4 ounces bittersweet chocolate with the 12 ounces semi-sweet chocolate.
Peanut Butter Chocolate Fondue: eliminate bittersweet chocolate and add 1/2 cup creamy peanut butter (NOT natural). You can stir in additional peanut butter once the chocolate has melted for even more "peanut butter" taste if desired.
Mexican Chocolate Fondue: add 1/2 teaspoon of cinnamon and ancho chili pepper.
Toffee Chocolate Fondue: add 1/4 cup toffee bits (Heath Bits O'Brickel) to the chocolate fondue.
Peppermint Chocolate Fondue: stir in 1 teaspoon peppermint extract to the chocolate fondue once it has melted. Add more to taste if you want a stronger peppermint flavor.