Typescript for Facebook React
The React team is currently discussing making Typescript annotations an internally used thing. This may be changing on the official for you, soon.
François de Campredon created a type definition for React: https://github.com/fdecampredon/react-observe-todomvc/blob/typescript/src/declarations/react.d.ts
It does not support JSX obviously, since it is another language with a syntax different from TypeScript.