I am very fond of Agatha Christie's work, although did not discover her properly until a few years ago. Now, I simply can't get enough. She basically invented the whodunnit and is responsible for most of the tropes we now know from the genre. Hell, any twist ending you can think of? She probably invented it.
Douglas Coupland is another author I admire greatly, as he is so in tune with the current attitude of the Western world, and indeed has been for over twenty years, that he's almost clairvoyant. I don't feel he gets enough recognition.
Another one with not nearly enough recognition is Jasper Fforde, who has created several incredible, intelligent worlds and series. If you love reading, love books, love stories, he is the man for you.
Finally, I greatly admire J. K. Rowling. Not necessarily for her novels because, while Jo can build an amazing world, and can produce characters in three dimensions every single time, she is not the best writer we've ever seen. However, she has spent much of her life during and since Potter working with charities and supporting reading programmes. We are indebted to her for making reading "cool" again and getting children to read. She will have my gratitude for the rest of time for that.