OK, on this one I am cheating again, because there are just so many amazing M's...
I first read The Handmaid's Tale in ninth grade, and it taught me to love women's fiction. For those of you that you haven't read it, this is one is a revolutionary and engrossing post-apocalyptic tale. As it is her most popular, I would also strongly suggest reading The Blind Assassin. Of the thousands of novels I've read, this one is one of my two favorites, ever.
Gabriel Garcia Marquez
If you read me gush about the enthralling voice of David Guterson, I bet he probably learned a thing or two from Marquez. If you want to read one of the most beautiful love stories of our time (coming from someone who adamantly despises reading romances), you must check out Love in the Time of Cholera.