The only marinade I have used is lime juice, olive oil, cumin, garlic, thyme and oregano.
Oh yum, that steak would never make it to the fajita stage! It doesn't need a darn thing other than a fork or two fingers to pick it up and eat it out of hand! Dang!I don't use a wet marinade on mine - I use a dry rub. I just mix up a bunch of seasonings and rub into the meat real well.
salt
pepper
various chili powders: ancho, chipolte, mixed, etc.
garlic powder
onion powder
oregano
smokey paprika
cayenne
You get the idea. Let it sit for anywhere from half an hour to a couple hours.