In a large bowl, combine cheeses; set aside 1 cup for topping. Add the beans, tomatoes, cream cheese, sour cream and taco seasoning to the remaining cheeses; stir until blended. Transfer mixture to a greased 2-qt. baking dish; sprinkle with reserved cheeses.
Bake, uncovered, at 350° for 20-25 minutes or until bubbly around the edges. Serve warm with chips and vegetables.