....I have always had a strong interest in pop sociology in my everyday life, and enjoy watching documentaries such as Fast Food Nation and Zeitgeist as well as reading texts such as No Logo and Affluenza. Zeitgeist, in particular, gave me a very insightful view of the way people, on a global scale, can be manipulated by large institutions, governments and economic powers. This is something I would like to explore further and studying sociology would give me this opportunity.
I would use FFN as a text, because it is a reasonably heavy text, and will demonstrate that you're capable of the hardcore reading req'd for Sociology. It is a prescribed text for a lot of first year sociology courses in the US.
If you want an additional doco, maybe go for The Corporation...?