Chris Voss' negotiation class has easily justified the $100 per year subscription. Kasparov's chess class is valuable, but it wouldn't be worth it on its own. Paul Krugman's economics class is interesting but pedantic. It only serves as a basic introduction, but does so in a field in which the introduction is barely useful. Tyler Cowen's Marginal Revolution University course fills the gap between beginner and intermediate economics for free.
