Butter one side of each bread slice. Top the unbuttered side of two of the bread slices with a slice each of Swiss, cheddar and havarti cheese. Top with the other slices of bread, buttered side up. Heat a non-stick skillet over medium heat. Add the sandwiches and grill 3 minutes per side, or until the cheese is melted and the bread is nicely toasted. Slice the sandwiches in half or quarters and serve.