Found this one on Chow and it was a great dipping sauce for homemade dumplings. I added a little bit of Sriracha for some zing.

•     1/3 cup light (regular) soy sauce
•     2 1/2 tablespoons unseasoned rice, Chinkiang, or balsamic vinegar
•     1/8 teaspoon sugar (optional)
•     Sriracha to taste
•     1 tablespoon finely shredded fresh ginger, or 2 teaspoons finely minced garlic (optional)

Combine the soy sauce, vinegar, and sugar in a bowl. Stir to dissolve the sugar. Taste and adjust the flavors to your liking for a tart-savory balance. Add as much chile oil as you like for some heat. The sauce can be prepared several hours in advance up to this point. Right before serving, add the ginger or garlic for a fresh layer of punch.