Twelve international criminal markets

I'm not confident of the data, but numbers one and two are drugs and human trafficking, and number five is human organs.
This from Transnational Crime In The Developing World: A February 2011 Report from Global Financial Integrity. The detailed report is here.

Roughly organized in terms of overall cash flow here is their list of goods illicitly traded across borders (the ordering depends not only on highly unreliable estimates, but on how the categories are aggregated...).

1. Drugs
2. Human trafficking
3. Illicit wildlife
4. Counterfeit goods and currency ("If imitation is the sincerest form of flattery, counterfeiting is the criminal form.")
5. Human organs (my worries about data sources are compounded by noting that their figures for legal US transplants come from a 2008 article in the Economist, rather than e.g. from UNOS/OPTN data, which is easily available on the web)
6. Small arms
7. Diamonds
8. Oil
9. Timber
10. Fish
11. Art and artifacts
12. Gold

From the executive summary:
"This report analyzes the scale, flow, profit distribution, and impact of 12 different types of illicit trade: drugs, humans, wildlife, counterfeit goods and currency, human organs, small arms, diamonds and colored gemstones, oil, timber, fish, art and cultural property, and gold. Though the specific characteristics of each market vary, in general it can be said that these profitable and complex criminal operations originate primarily in developing countries, thrive in the space created by poverty, inequality, and state weakness, and contribute to forestalling economic prosperity for billions of people in countries across the world.

"The global illicit flow of goods, guns, people, and natural resources is estimated at approximately $650 billion. Though data is scarce and experts are constantly debating the relative merits and weaknesses of every new study, it is generally accepted that illicit drug trafficking and counterfeiting are the two most valuable markets. This report finds the illicit drug trade to be worth roughly $320 billion and counterfeiting $250 billion. These numbers reflect the potential for huge profits which is
the fundamental driver of criminal trade."

HT: Bettina Klaus