If you're buying them from the store, any of the following are decent:
- Teriyaki sauce/marinade
- Chili garlic sauce
- Chili black bean sauce
- Hoisin sauce
- Satay (peanut) sauce
However, it's really a lot tastier (and cheaper!) if you make it yourself. I usually use some variation on the following:
- 3/4 cup water
- 1-2 tbsp dark soy sauce
- 2-3 tbsp light soy sauce or teriyaki
- 1-2 tbsp toasted sesame oil
- (optional) 1-2 tsp chili oil
- 1 tbsp tapioca starch (test a bit of sauce; if it doesn't thicken right, add more)
- Minced or grated ginger, to taste
- Minced or grated garlic, to taste
- 1/2 tsp brown sugar, honey or maple syrup
The proportions are all pretty rough because I always eyeball it, and because ingredients vary (I can't always get the same brands or sometimes I'm missing one or two). I kind of eked out this formula after a few years of stir-frying, so I don't even really think about it anymore. It usually tastes great though, and I've even gotten several comments to the effect that it smells great (I think the sesame oil is what does it).
P.S. You can substitute corn starch for tapioca, but you'll have to use a little more of it, and the sauce doesn't tend to be quite as smooth or consistent. It'll work in a pinch, though, or if you can't find tapioca in your area.
P.P.S. When I make this, it usually makes a little more than a cup. What I tend to do is marinate and stir-fry the meat separately in a separate, simpler sauce (honey teriyaki works great), then half-stir-fry and half-steam the vegetables using half the sauce, so they get nice and tender. Then add the meat and the rest of the sauce and stir fry for about a minute or two longer. This gives you a nice balance of flavour infusion and extra sauce that you can use for rice.