I got this marinade recipe from the mother of a friend of mine.
Its really, really good, just make sure that you use the right cut, I definitely suggest using a London Broil cut with this, and that you marinate for the proper length.
3/4 cup olive oil
1/2 cup soy sauce
2 Tablespoons Worcestershire sauce
1 Tablespoon dry mustard
2 teaspoons garlic salt
1 teaspoon pepper
1/4 cup red wine vinegar
1 teaspoon parsley flakes
1/4 cup lemon juice
Combine all in a large ziploc plastic bag and marinate the meats overnight.