I have made London broil for years and until recently, have never really cared for it. I finally found a marinade that is tasty and figured out the grilling technique and timing so it's just right, not over cooked and dried out.

London Broil Marinade

1/4 cup balsamic vinegar
1/4 cup soy sauce
1/4 cup olive oil
splash of Worcestershire sauce
sprinkle of rosemary
2 tbsp minced garlic
dash of black pepper
London broil beef

Night before I want to serve it, I mix all the ingredients in a glass dish (or you can use a plastic Ziploc bag). I stab my beef with a fork on both side. I move it around in the marinade to coat it well on all sides. Set in fridge to marinate. Next morning, about 10 hours before cooking, I toss again and leave it to marinate on the other side. When I come home in the evening, I pull it out and set on counter to get to room temperature (about 20 minutes before firing up the grill). Heat grill to 350-375. Place meat on grill (discard any leftover marinade). 4 minutes each side. Remove and put on a cutting board and let set 10 minutes before slicing. It comes out a perfect medium rare-medium temperature.

Don't be afraid to only cook it for 4 minutes on each side -- it continues to cook while it sits before you cut it.