This is an expanded version of Carroll’s lecture notes on relativity, which he has used to teach courses and which are available for free online (see the “Lecture Notes” tab on the page linked to above). I find it to be an excellent introduction to the subject, which covers the mathematical tools used, the basics of the theory, and the most common applications, all in a straightforward fashion. I have recommended this text (or its corresponding lecture notes) many times on Physics Forums as a reference for people who want a good introduction to the subject.
Other Textbooks Read:
Spacetime Physics, by Taylor & Wheeler. The text that I first learned Special Relativity from, and still a good introduction, with an emphasis on building physical intuition. However, it does not cover General Relativity. (Taylor apparently has a follow-on text covering GR at least as it applies to black holes, but I have not read it.)
Gravitation, by Misner, Thorne, & Wheeler: The classic text, and still a good comprehensive reference even though it was published in 1973. However, it is very comprehensive and detailed, has a somewhat idiosyncratic style, and can be difficult if you don’t already have considerable background in the subject. It also weighs enough to seem like it might undergo gravitational collapse and become a black hole. :-)
General Relativity, by Robert Wald. Another classic, with a more abstract mathematical approach than MTW, not as comprehensive but covering some topics in more detail and from a different viewpoint than MTW. Published in 1984, so it also covers some topics, such as quantum fields in curved spacetime, that were too new to be covered when MTW was published. Not as recent as Carroll’s text (published in 1984), and going into topics that are probably too advanced for readers who are being introduced to the topic for the first time.
The Large Scale Structure of Spacetime, by Hawking & Ellis. The definitive text on global geometric methods and causal structure in GR. It covers the classic singularity theorems of Hawking & Penrose in detail. However, it is really a monograph, not a comprehensive GR text, and requires the reader to already have considerable background in the subject.
The Usenet Physics FAQ has a long list of relativity references here:
Relativity
Recommendation: Spacetime and Geometry
Author: Sean Carroll
This is an expanded version of Carroll’s lecture notes on relativity, which he has used to teach courses and which are available for free online (see the “Lecture Notes” tab on the page linked to above). I find it to be an excellent introduction to the subject, which covers the mathematical tools used, the basics of the theory, and the most common applications, all in a straightforward fashion. I have recommended this text (or its corresponding lecture notes) many times on Physics Forums as a reference for people who want a good introduction to the subject.
Other Textbooks Read:
Spacetime Physics, by Taylor & Wheeler. The text that I first learned Special Relativity from, and still a good introduction, with an emphasis on building physical intuition. However, it does not cover General Relativity. (Taylor apparently has a follow-on text covering GR at least as it applies to black holes, but I have not read it.)
Gravitation, by Misner, Thorne, & Wheeler: The classic text, and still a good comprehensive reference even though it was published in 1973. However, it is very comprehensive and detailed, has a somewhat idiosyncratic style, and can be difficult if you don’t already have considerable background in the subject. It also weighs enough to seem like it might undergo gravitational collapse and become a black hole. :-)
General Relativity, by Robert Wald. Another classic, with a more abstract mathematical approach than MTW, not as comprehensive but covering some topics in more detail and from a different viewpoint than MTW. Published in 1984, so it also covers some topics, such as quantum fields in curved spacetime, that were too new to be covered when MTW was published. Not as recent as Carroll’s text (published in 1984), and going into topics that are probably too advanced for readers who are being introduced to the topic for the first time.
The Large Scale Structure of Spacetime, by Hawking & Ellis. The definitive text on global geometric methods and causal structure in GR. It covers the classic singularity theorems of Hawking & Penrose in detail. However, it is really a monograph, not a comprehensive GR text, and requires the reader to already have considerable background in the subject.
The Usenet Physics FAQ has a long list of relativity references here:
http://math.ucr.edu/home/baez/physics/Administrivia/rel_booklist.html