Relativity:The Special and the General Theory
The book starts with a look at classical physics and geometry, and describes how the propagation of light didn't fit in to the principles of relativity found elsewhere in physics. Einstein then introduces his famous argument involving lightning strikes seen from a train and from the ground and goes on to derive the equations of special relativity. This is followed by an explanation of how space and time become united into four-dimensional spacetime.
The second part of the book moves on to general relativity, looking at curvature in space and space time, and discussing the equivalence principle and it's consequences. This is followed by a discussion of the models of the universe which can be obtained from GR (although this was before most of the work in this area). There are several appendices, including one with a discussion of the nature of space.
There is some of the usual mathematics for the derivation of SR, but the later parts of the book are wholly non-mathematical. The book will be of historical interest to those who have learnt about relativity, but I think it will also be of interest to novices in the subject who can thus find out what relativity is about.