If you know anyone from San Francisco or New York, you've probably heard them complain about the cost of their rent. And if you live in one of those cities, you're probably used to friends from home visiting — and boasting about how much more living space they have for half the cost of your apartment.Of course, for many people who live in urban areas, the quality of life outweighs having a small living space . (Hey, the city is your playground, right?) Still, it does sting to look at how much more affordable other places are.But whether or not you live in an expensive city, it's always interesting to look at what others pay in rent. We decided to look at Apartment List's December report on which cities are the most expensive to rent an apartment in the United States. The rankings are based on the median price of a two-bedroom rental in each city.Unsurprisingly, urban areas like San Francisco, New York, and Boston topped the list. And if you're looking for an affordable rental, you might not want to move to California — six of its cities made the list of the top 15 most-expensive rentals.Click through to see the median price for what people across the country are really paying in rent each month.