Oh boy. This is picking up in the news, but has been an issue on the Ivory Coast for years (Cadbury chocolates stopped doing business in the Ivory Coast because of this about 50 years ago).
Here's a site that can give you an overview (warning: there are a few graphic images tucked away in places on the site). Also, just know going in that this guy is pretty angry and some of his comments are a little over the top. I will say, though, that this is not a political issue, as far as I'm concerned. It's a spiritual one. Perhaps the corporations involved are well-meaning but ignorant (I doubt it). I have no doubt, however, that the American chocolate-buying public has been unaware of it, and that together we can bring freedom to the slaves in this industry.
Here are some slavery-free chocolate companies.