Let the Right One In (2008)
An extremely effective story of two neighbor children, both lonely outcasts, becoming close friends. It seems as though the lack of other options is what forces them together, but that doesn't mean that they're not perfectly matched -- giving each other the acceptance and dependence so desperately craved by both.
That one of them is a vampire is, of course, a huge hook -- but it's a testament to the tone and style that what I remember most about the film is the relationship between these two kids, their palpable loneliness, and the way they change into something stronger when together.
B+