Wikipedia's list for her publications is accurate:
- Fantastic Beasts and Where to Find Them (supplement to the Harry Potter series) (1 March 2001)
- Quidditch Through the Ages (supplement to the Harry Potter series) (1 March 2001)
- The Tales of Beedle the Bard (supplement to the Harry Potter series) (4 December 2008)
In addition to that, she writes the articles found on Pottermore, which not only adds background details to the Potterverse, but has also released information about events after the series. Not all content on the website is authored by her, however. For a more complete breakdown of her online and digital works, see @ibid's answer.
She is also a regular user of Twitter, and more than once has posted new Word of God canon through her tweets and not elsewhere.
Rowling has also been said to have written the story for the new Harry Potter play, Harry Potter and the Cursed Child, but the story is also credited to Jack Thorne and John Tiffany. (Thanks to @JasonBaker for the reminder.)
She also wrote the screenplay, as mentioned by @DVK, for Fantastic Beasts and Where to Find Them the movie, based loosely on the book (or more accurately, the character said to have written that book In-Universe, Newt Scamander).
A spin-off/prequel of the Harry Potter film series and directed by David Yates, the film was written by Rowling as her screenwriting debut. It is the first installment of a trilogy. Rowling produced the film alongside David Heyman, Steve Kloves, and Lionel Wigram.