Prices of other related goods
i) Substitutes: If X and Y are substitutes, then if the price X increases, the quantity demanded of X falls. This will lead to increased demand for Y, and this way eventually lead to increased supply of Y.
ii) Complements: If two commodities, say A and B are used jointly, then an increase in the price of A shall lead to a fall in the demand for A, which will cause the demand for B to fall too.