My introduction was "Mindfulness in Plain English" by Henepola Gunaratana. Gets you practicing right away while subtly introducing Buddhist ideas.
I've also heard "Being Nobody Going Nowhere" by Ayya Khema is a good introduction. I read it a few years in, but it's still an excellent book that covers all the basics.
"The Heart of the Buddha's Teaching" by Thich Nhat Hanh is great. It's a bit dense. I'd just read that a chapter at a time.