What are some common distributions assumed for approximating a demand curve?

Question

A demand curve is a function $d(p)$ such that at price $p$ the demand for the good is given by $d(p)$. This means that you are making a sales of $p\cdot d(p)$ at price $p$. For typical goods, demand drops as price increases, ultimately vanishing at $p=\infty $. What are some of the functional forms commonly assumed here? Of course assuming a functional form will put certain constraints on the elasticity and such, and that is understood.