I linked this one because for some reason I don't see it being mentioned more often. It is concise and manages to pack in a lot of problems that really develop your tensor calculus calculation skills in the setting of relativity and the later discussions on causality and cosmology are really cool but the book isn't as advanced as Wald or Carroll. The book is used for the course taught at Oxford to senior level applied mathematics majors but I'm sure physics majors can use it too (I'm a physics major and I like it mainly for the utility of the problems in making the calculations required in Wald etc. much more fluid to do and simply because these kind of tensor calculus problems are fun and this book has a ton of them whereas other standard GR books really don't other than MTW). It is awesome in a supplementary nature.