I agree with the sf pudding powder! But I think the consensus was that it wasn't permitted on Phase 1. There was a big discussion about it a while ago. [ETA: oh here is a sticky about it Are SF Puddings and yogurt allowed on Phase 1?
I sometimes add sf hot chocolate powder but I'm pretty sure that is not for Phase 1 either, sorry.
Here are a couple of ideas though:
Sweet variations: I have added various flavors of Crystal Light or Torani syrups (sf vanilla and sf coconut are my favorites). I'm not a fan of the fake sweeteners, but what can I say, they are good in a pinch.
Savory: I love garlic yogurt. One of my favorite ways to eat Greek yogurt is to add some crushed garlic, a little salt, and a lot of chopped up or grated cucumbers (much like CyndiM said, but with garlic), sometimes even a little chopped walnut. My ratio is 1 cup of Greek yogurt to 1/2 to a whole English cucumber. I often eat it inside bell pepper "boats" - so good!
Also, Trader Joe's onion dip mix *might* be OK made with Greek yogurt? I can't find my packet to check... if anyone has the ingredients, please post. The dip is delicious with raw veggies, but I have no idea if it is Phase 1 or even Phase 2 - compliant.