The French Quarter of New Orleans smells like vomit and fermented daquiris that have been spilled on the sidewalk. Even though Bourbon Street is regularly hosed down shortly after dawn, it does little to diminish the smell, which was the main reason I usually walked down Decatur Street instead.
Vancouver, Washington often smells like boiled broccoli, an unfortunate by-product of the paper pulp mills in the area. It's even worse further north, as evidenced by the catchphrase "the aroma of Tacoma". Fortunately, the mills have worked hard and spent a lot of money to reduce their emissions and the resulting stench.
After moving to Portland, I was saddened to learn that rain doesn't smell as magical here is it does in the unpopulated deserts on the outskirts of Phoenix. I finally found out at a botanical garden that the smell was coming from creosote bushes, which are still plentiful in the undeveloped deserts.