Terry Pratchett is an excellent author, not only because his imagination created the magical Discworld, but also because he can write. I mean, really write. He understands grammar. He knows how to structure the piece. And his trademark sense of humour doesn't hurt, either.
A Slip of the Keyboard is a worthwhile collection of his non-fiction: articles, speeches, musings. From topics as diverse as Alien Christmas and Old Timers Disease (read the book to find out), he spins an enchanted web with which to capture his readers.
If you love Discworld, read this book, too.