Read the obituary at U of Texas at Austin. They are also putting all his EWD manuscripts online. These are must reads.
I remember at my first class at first year of computing science at Imperial, the professor said, learn to spell Dijkstra. Otherwise you will never pass any exams here. Dijkstra contributed so much pure thinking in the field of computing science. He shall be missed.
A few quotes from him: Aim for brevity while avoiding jargon, and Progress is possible only if we train ourselves to think about programs without thinking of them as pieces of executable code.