Prison guard unions would be one. The War on Drugs is a major contributor to the sad statistic that the US has more prisoners than any other country on the planet (not per capita, more prisoners, period). That means good business for prison guards, and the prison guard union wields a disproportionate amount of power, at least in California.
One possibility: big financial institutions. Michael Rupert has done a lot of work in this area. IIRC, the illicit drug trade is the world's largest commodity market -- bigger than oil. That money has to go somewhere, and wherever it goes it is bound to be massively influential. Rupert argues that the links to big financial institutions are often quite clear, and he backs up his arguments with fairly prodigious research.
Aside from the prison/leo system mentioned below, Drug cartels have a vested interest in the continued war on drugs. There is no way they could reap the profits they currently get in any other way.
The Correctional Peace Officer union is the second strongest/most powerful union in California (behind California Teachers Association). Privatized prisons also contribute great deals of money to political candidates.
Keeping the prisons full simply means arresting people for behavioral mopery instead of pharmaceutical mopery. As long as the public supports a high incarceration rate, the prison guards unions have a license to print money.
And police departments and officers should likewise dislike the War on Drugs. It takes low staffing levels to investigate whether people have crack in their pockets. Doing, you know, actual investigations of crimes requires considerably higher staffing, plus the toys are way cooler.
Actually, LOTS of people benefit. In no particular order:
1) Wackenhut (GEO group), private prison operator, and the entire prison complex (guard's unions etc)
2) Law enforcement. Even if the DEA had a 99% interception rate, that economics of the trade mean that it is still profitable at 1% supply. Hence, no matter how many busts the DEA makes, they will always need more resources/money/helicopters etc.
3) Banking and Finance. Drug money is the global financial system's liquidity float. It kept Wachovia solvent for nearly a decade.
4) The US Treasury. Do your own research. Suffice it to say, opium production in Afghanistan now exceeds pre-Taliban levels.
This indicates to me that there might be a strong connection between the prison-industrial-complex and the military-industrial-complex with that connection being drugs. Meanwhile, Big Finance amorally profits from all (including illegal) activity.
