This is a combination of several recipes that Jay found online for London Broil. Use this method for cuts of beef that are less expensive and likely to be a little tougher.
 

Marinade Ingredients:
2 teaspoons seasoned meat tenderizer (or juice of 1 lemon)
4 Tablespoons (1/4 cup) sherry
1 Tablespoon soy sauce
1 Tablespoon honey
1/2 teaspoon salt
½ teaspoon monosodium glutamate 
 

Pierce the surface of the meat at 1-inch intervals with a sharp fork – place in Ziploc bag and pour marinade over meat. Refrigerate for an hour, turning over after 30 minutes.

While the meat is marinating, prepare the sauce by combining all the ingredients:

Sauce Ingredients:
½ cup butter (1 stick)
¼ cup beef broth concentrate
¼ cup red wine
1 teaspoon Worcestershire sauce
2 Tablespoons parsley, chopped fine
1 Tablespoon scallions, chopped
 

Place meat on grill and brush with marinade. Cook 10-20 minutes on each side depending on thickness and desired doneness. Brush on remaining marinade after turning. (If you broil instead of grilling, use a meat thermometer and cook to 120 degrees. Meat will be rare to medium rare.)

Remove to cutting board and slice meat diagonally into thin (1/4-inch) slices. Drizzle with some of the sauce and serve with remainder of sauce in small pitcher or bowl.