A pretty popular marinade in these "Mo" parts (aka Mormon community) is the classic bottle of Italian dressing. You can't open a ward cook book without Italian dressing not being mentioned in two or three recipes. I am not knocking the Italian dressing marinade, it is a valid marinade, and I will tell you why. There are 3 things all marinades need.
1. oil. Oil enhances the flavor and bastes the meat.
2. an acid, (vinegar, citrus, wine, buttermilk, yogurt) acids act as the tenderizer
3. seasoning (salt, pepper, soy sauce, Worcestershire sauce, spices, garlic, onion).
Italian dressing has all three things right? So it works. If you are using highly acidic things for your marinade, overnight marinading is too long. Keeping meats in marinade for too long will essentially be cooked by the acid. Things like buttermilk, yogurt, sour cream are good to marinade overnight in. Fish should only be marinade for 30 minutes to 1 hour.
So for the London broil I marinated it in equal parts olive oil, and balsamic vinegar, 4 smashed garlic cloves, 2 or three tablespoons of Worcestershire sauce, couple teaspoons of salt and pepper, a couple teaspoons of steak seasoning (costco), 3-4 tablespoons of soy sauce, and 3-4 tablespoons of sugar ( I don't know why, I just thought it would be good). I mixed it all in a bag and added the London broil and kept it in the fridge for about 6 hours. Before I grilled it, I scraped everything off ( the garlic will burn) and it was delish!
So as far as marinating goes, you can play with just about anything, just remember the three key points. Or just stick to the Italian dressing, if you are lame!