Preheat oven to 350°F (175°C).
In a large bowl, combine softened cream cheese, mayonnaise, and sour cream. Mix until smooth.
Stir in Monterey Jack cheese, Parmesan cheese, crab meat, green onions, lemon juice, Old Bay seasoning, garlic powder, black pepper, and cayenne pepper (if using). Mix until well combined.
Pour crab dip mixture into a greased oven-safe dish or pie plate.
Bake for 20-25 minutes, or until heated through and bubbly around the edges.
Serve hot with tortilla chips or crackers.