What are food combinations that trick your taste buds into tasting sweet? I recently tried unflavored yoghurt with a teaspoon of cinnamon, and for some reason, the combination tasted sweet. Are there any food combinations that accomplish this? 

The yoghurt was non-fat; I'm assuming that because both ingredients contained carbs consequently any other combinations that also work would perhaps need to be 'carby' ingredients.

The nutrition facts of the yoghurt per 100 ml:

energy: 21 kcal

protein: 1.8 g

carbohydrates: 2.8 g

fat: 0.3 g

sodium: 0.25 g
Though your yogurt was unflavored, it almost certainly still contained lactose (milk sugar), so it should still taste a bit sweet regardless of whatever was added to it. And as Catija points out, "unflavored" doesn't apply to added sugar, of which there can be quite a lot in yogurt (and almost every other prepared food).