I am not a big fan of strict recipes for things like marinades, because the thickness of the meat* (yes, meat! What else is there to marinate?) and the amount of water in it can affect how quickly the marinade flavors it. For instance, if I were marinating something very thick I would use more salt than if the meat were cut thinner. I speak from bitter…er, salty experience, most recently last night.
Anyway, I have a fallback marinade that works very well with pretty much everything, but because it seems like a summery mixture I tend to use it when I barbecue, and that is usually during the summer. I love the flavor of chipotle, which is smoked jalapeños, usually found canned in an adobo (which means seasoning in Spanish). So all I do is grab a few peppers out of the can, and if I have wimpy guests I scrape the veins and seeds out of them. The sauce is pretty good too, so slosh a bit into the marinade. Using a hand blender I puree the peppers with some garlic, parsley (or cilantro), a bit of salt, and lime juice. Then I emulsify it with olive oil. Flank steak seems to suck up this stuff pretty quickly, and because the steak is pretty thin it grills in a matter of minutes. The marinade lasts for several days (maybe years, but I use it too quickly) in the refrigerator, so make a big batch and experiment.
*PETA: People Eating Tasty Animals