Cut crust off all sides of bread. But in 1-1/2 inch cubes, set aside. In a large saucepan, melt butter. Stir in cream cheese until melted. Remove from the heat; stir in cheddar cheese and blue cheese until melted.
In a small mixing bowl, beat egg whites until stiff peaks form. Fold into cheese mixture. Dip bread cubes into cheese mixture. turning to coat.
Place on greased baking sheets, sprinkle with paprika.
Bake at 375 degrees for 12-15 minutes or until bottoms are golden brown. Serve warm.