I also wrote a GR book: “Relativity Gravitation & Cosmology: a Basic Introduction” (Oxford Masters Series in Physics). It is an introduction to Einstein’s general theory of relativity for readers with an undergraduate math background, and includes discussion of recent development in cosmology, issues like dark matter, dark energy, and the accelerating universe, etc. In the second edition (published in 2010), most chapters have been revised; I have also added one new chapter on special relativity (to make it clearer the meaning of a geometric formulation of SR) and one on black holes (the full power and glory of GR), as well as updated on most recent GR tests and latest cosmological data. Here is a PDF file of my most recent talk on Dark Matter and Dark Eenergy.