Not sure if it's been posted before, but this series of lectures is simply awesome. Conducted by none other than Leonard Susskind (Mr String Theory himself), he often gives out tip-bits on the history and evolution of GR.
I've pasted it here because several people have commented on this forum that they would like to know more about it, but feel the math is beyond them. All I can say is; don't worry about the math, although tough in parts, you'll pick up the gist as he goes along regardless - his presentation is that good.
http://www.youtube.com/watch?v=hbmf0bB38h0
Reckon I might turn this series into a DVD for keep-sake and as a reference.
So glad Stanford (somebody) decided to do this. Hats off to them.