As far as GR, I'll second the vote for Gravitation, by Meisner, Thorne, and Wheeler.

Been teaching myself GR (slowly) out of it. IT's not absolutely perfect, but it's a very very very good text.

As far as the level of math, it uses some high level stuff, but it builds it up.

I do wish someone had constructed a solutions guide for problems in that text though. There're a couple of exercizes that are more or less the only places certain derivations are dealt with for things that are important later.

And some of those things I had/have a bunch of trouble solving. But still, it really is a good text. Besides, it uses the word "antibongs" (in the context of talking about one-forms)

Warning: the text is a bit of an empirical one. That is, it's large and heavy enough that you can do direct observations of the effects of curvature of spacetime. :D