Parable of the Sower and Parable of the Talents, Octavia Butler (1993 and 1998, respectively)
(I've allowed myself well over 100 words here since i'm covering two books in one note.)
I devoured the first book, thinking all the way through that i will likely teach it in my literature course next spring. The second book went slower because it is so harrowing. I had to force myself through parts of it, not because it is poorly written — far from it — but because what happens to the main character is so upsetting. Toward the end, i picked up speed again. Despite the disappointment of knowing that Butler intended to write a third book but died before she completed it, this series is immensely satisfying. No surprise that people have been inspired to create real-world communities based on the principles she develops in these books. They are usually classed as works of science fiction, but they would be a great first step into the genre for curious non-aficionados: no intimidating other-worldly jargon to master; no challenges to suspension-of-disbelief that you wouldn't find in most fiction, sci-fi or not; and lots to think about with respect to the world outside the books.