What's the best overnight marinade for grilled chicken tacos?

My mom always uses italian salad dressing as the marinade for fajitas.

I find the simpler the better because the things you put in a taco are so flavorful. I don't marinate overnight, but you could if you don't use citrus juice. I like a little oil, cumin, nacho or chipotles chili powder, like zest, garlic and salt and pepper.