Dang. Thought I had come up with this delicious little marinade on my own, but as it turns out, I've made it before.
Here is Giada's roasted chicken with balsamic vinaigrette recipe. Anyone else wish Everyday Italian would come back? Anyway. I somehow did this one from memory, almost exactly, when I was getting ready to grill some chicken tonight that would adorn the top of a big plate of angel hair dressed in my makeshift pesto.
My marinade (which I think would make a dang fine salad dressing) was to squeeze into a bowl the juice of half a lemon, about 1/4 cup balsamic vinegar, good pinch of salt, pepper, some honey, and some dijon mustard, whisking in some extra virgin olive oil at the end (yielded about 2/3 cup of marinade/dressing... adjust ingredients to your liking).
Pour over some chicken breasts (may want to save some of the marinade to dress chicken with post-grilling), marinate in fridge for 30 minutes. Grill. Enjoy.