Second the MX Master! It's a great mouse.

Like Jill Castro has said, the React project itself is exemplary . However, If you're looking for projects that are built with React, I can highly recommend this list. Just by scrolling through it you'll notice a lot of big-name companies. A lot of them have their code open-sourced. I personally really like the Khan Academy repository.

This! It's an amazingly well-organized project.