The react site itself has a very good getting started tutorial but I also found a few quality blogs that were useful for getting quick overviews and a better understanding.
- React Getting Started Tutorial
The official guide is comprehensive and very professionally finished. You might want to start with some of the other light weight tutorials if you just want a quick overview.
- Learn React Videos
Very short (2 minutes each) videos of React basics. Fastest way to get a feel for the library without reading through a lot of text.
- ReactJS Tutorial
Tyler McGinnis provides a great step by step tutorial in this first of several guides. I worked my way through these for my ReactJS refresh session and found it very useful.
- Getting Started with React
Ryan Clark’s nice little dropdown menu system using ReactJS. Takes you through the steps and shows a slightly more complex real world UI solution.
- D3 and React for Charting
A little out of date and I only managed to get the first chart sample to work (after updating the __owner__ to _owner) but still gives you an idea of how to mix these two libraries.
I put a few static pages together using some of the tutorials above, you can find them under my research-html project on GitHub.