Any communist/Marxist literature :p Maybe have a browse around on ProleWiki. I would also recommend Socialism: Utopian and Scientific by Friedrich Engels, because I think it does a good job of explaining the basics in the last chapter (but the first two are worth reading too). For something less theoretical that just tells it how it is right now, I would recommend "Confessions of an Economic hitman", which exposes the meddling of US imperialism around the world (including politics)

Most of the Marxist literature can be found on Marxists.org