I just finished reading this book, called "
God's Equation", by Amir D. Aczel (a mathematician).
Quite an interesting book - focused on Einstein, and his life and work around the field equation, and the general theory of relativity.
It's aimed at a general audience, but quite of a lot of it is Math's heavy and a lot of the explanations and theories went over my head. Still, I found it a very interesting read, learning about Einstein's life, and how he tried to prove the equation (unsuccessfuly) during the Solar eclipse of 1914.
It was Eddington in 1919 who used another Solar Eclipse to prove the equation, but taking photos of the background stars in Hydra during totality, and measured them against plates developed at other times to see how the position of the stars changed as light was "bent" around the massive object (the sun).
Some good information about modern cosmological thinking towards the back (the book was written in 1999, so it's a little outdated already).
I found a short (good) review here.
Not a bad read, especially if you're into cosmology and have some understanding of the maths and theories involved.