Here are some components and utils that will make your React developement even more enjoyable.
Feature rich, configurable date picker for react. Worked everytime without any issue.
Drag and drop is not so easy to handle. React Dnd makes it easy with React.
When you want a code editor in your react app, React Ace is the package you want. React ace is a wrapper for Ace editor.
Modal dialog in react.
Skylight makes modal dialogs easy, which is something I discovered recently.
Ok, I snuck one of mine in! Dazzle makes building dashboards easier.
Working with CSS classes could be tricky when you want to append and remove based on conditions. If you have a requiment to work with classes, this package is a must.
Axios is a promise based HTTP client. Very nice API and I really enjoyed working with this library. You might also want to check axios mock adapter which makes testing easier.
If you are writting tests for your react components, which you should, do your self a favour and use Enzyme.
As a developer, working with CSS to get things to look the way I wanted was always challenging. Things changed when I discovered Semantic UI. An awesome set of UI elements to pick from and they compose extremly well. Semantic UI is also getting its official React components here. Keep an eye for it as well.