Here is the recipe I used:
1/2 tsp. dish soap
1 tsp. baking soda
2 tbsp. white vinegar
2 cups water
3 drops oil (I added a couple extra drops)
I mixed everything except the oil in a bowl, and then added the oil into the spray bottles before adding the rest of the liquid. That way I could add whatever oils I wanted to combine and make each bottle different. I made some simple labels out of decorative paper. These would make great presents, especially if you used scents your receiver likes.