Geroch's lectures on General Relativity gives (what I consider) a novel approach to the subject, by giving a physical introduction of concepts - unlike most books, which start with a mathematical machinery -, a clear example of this approach is the argumentation for the introduction of spacetime and the necessity of the structure of manifold on it.
The contents of the book range from the basics of spacetime, world-lines, clocks and light-cones, up to some introductory topics of causal structure, asymptotic limits, and even quantization of gravity.
I believe that any person interested in gravitation MUST study this book at certain point of its academic life, specially because it is not only about the subject, but the carefully presented train of thought of one of the brightest scientists on the area.