If you're new to React this is also a great article to check out. Ryan walks through everything from JSX and the virtual DOM to state and props + more.
If you're coming to React from an Angular background, you should check out this article. Micah walks through his thoughts on making the transition to React.
If Dan writes something, you should probably take some time to read it. He produces some really good material. In this article Dan talks about when you should, and shouldn't use Flux in your projects and expounds on the dangers of dogmas in upcoming technologies.