"In the Buddha's Words" by Bhikkhu Bodhi. The PDF version of it can be downloaded here.
It is an anthology or selection of translated suttas from the Pali Canon. It is also thematically and systematically arranged.
I highly recommend this book to anyone who finds the Sutta Pitaka too huge and difficult to traverse. Bhikkhu Bodhi is one of the foremost translators and scholars of the Pali Canon. He also created this 512-page anthology arranged in a systematic manner, for the benefit of Pali Canon students everywhere.
I quote from the Preface:
In an ongoing series of lectures I began giving at Bodhi Monastery in
New Jersey in January 2003, I devised a scheme of my own to organize
the contents of the Majjhima Nikaya. This scheme unfolds the Buddha's
message progressively, from the simple to the difficult, from the
elementary to the profound. Upon reflection, I saw that this scheme
could be applied not only to the Majjhima Nikaya, but to the four
Nikayas as a whole. The present book organizes suttas selected from
all four Nikayas within this thematic and progressive framework.
This book is intended for two types of readers. The first are those
not yet acquainted with the Buddha's discourses who feel the need for
a systematic introduction. For such readers, any of the Nikayas is
bound to appear opaque. All four of them, viewed at once, may seem
like a jungle—entangling and bewildering, full of unknown beasts—or
like the great ocean—vast, tumultuous, and forbidding. I hope that
this book will serve as a map to help them wend their way through the
jungle of the suttas or as a sturdy ship to carry them across the
ocean of the Dhamma.
The second type of readers for whom this book is meant are those,
already acquainted with the suttas, who still cannot see how they fit
together into an intelligible whole. For such readers, individual
suttas may be comprehensible in themselves, but the texts in their
totality appear like pieces of a jigsaw puzzle scattered across a
table. Once one understands the scheme in this book, one should come
away with a clear idea of the architecture of the teaching. Then, with
a little reflection, one should be able to determine the place any
sutta occupies in the edifice of the Dhamma, whether or not it has
been included in this anthology.