To break down some favorites by a few countries:

Japan: for a country in which I love so much of the food scene, I don't think its cities have the greatest scents...too much salaryman and stale cigarette permeate older buildings. Still, the warayaki in Kochi, bakeries throughout the depachika, and steeped genmaicha come to mind.

Mexico: chocolate at various cafés, coffee throughout the south, and tacos al pastor. Gracias, Lebanon!

China: yeah, right! Buuuut, I do get easily tempted by the cuminy soups of Lanzhou lamian eateries, and of course the streetside bbq, in particular the garlicky spicy vegetables and mantou.