Preheat the oven to 350°F (175°C).
In a large bowl, mix together the softened cream cheese, mayonnaise, and sour cream until smooth.
Fold in the corn, Monterey Jack cheese, cheddar cheese, green onions, garlic powder, black pepper, and cayenne (if using).
Transfer the mixture into a baking dish and spread evenly.
Bake for 25-30 minutes, or until hot and bubbly with a golden top.
Serve warm with tortilla chips, crackers, or veggies.