This recipe was in Martha Stewart Living and I think it is a good basic marinade. She uses it in a recipe for Steak and Arugula Picnic sandwiches but I just marinated my steak and served it on arugula with some potatoes on the side. The important tip is to slice your meat across the grain, not along it. It makes a big difference!!
1/2 cup balsamic vinegar
1/4 cup soy sauce
2 T. brown sugar
4 garlic cloves, sliced
1 T. chopped rosemary
coarse salt and pepper
1 # skirt steak (I could only find flap)
Poke the steak all over with a fork. Combine marinade ingredients in an airtight container (i used a ziploc) and add to marinade for at least 30 minutes or you can marinate it overnight.
You can broil(or 500 degrees) this on a foil lined baking sheet or grill it. Broil the steak 3 minutes on each side for medium. Cook an extra minute or so on each side for more well done.
Let the meat cool 5 minutes before slicing. Slice against the grain of the meat.