The Economist produced a chart that looked at estimates of the size of various black markets:

• Drug trafficking is worth an annual $320 billion a year and is thought to be by far the largest black market in the world.
• 21% smaller is the second placed market for counterfeit and pirated goods, worth $250 billion.
• Human trafficking is worth $32 billion and is 68% bigger than the market for wildlife trafficking. Human organ trafficking is worth $0.6 billion.
• The numbers are inexact and come from various years. The estimates are based, in part, on seizures by border control agents.

Read more about other markets and their comparative size, in a striking chart over here.

Source: The Economist