I do something like YourName2000's basic [Red wine (or port) with a bit of garlic powder, black pepper, spices if ya want, is pretty easy, sugar free and reliable.] and then add about two teaspoons of olive oil and a few good shakes of Worcestershire. Or you could mush up a couple of anchovy filets in it. The anchovy taste fades but is helps blend flavors.
Also a fish marinade for reference: rice wine vinegar, sliced ginger, garlic, sliced green onion, soy sauce and a touch of oil. Does great things for grilled salmon or even chicken.