Georg Simmel, a contemporary of Max Weber, to my mind is a very underrated classical sociologist. In this very remarkable book Simmel discusses money from several angles. 
Simmel sees money as an important medium in the creation of social ties. Through money, relationships between people are established and given content and form. At the same time, the money aspect of social ties provides a basis for intellectualization processes and the disintegration of substance into impersonal ties. Tendencies to calculation and numerical analyses, as well as money’s tendency to become an end in itself, give money based relationships a set of extremely dynamic properties.
The Philosophy of Money is a good book to start with for readers wanting to take a closer look at this original and important social theorist.
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