First of all, I hope you own Andrew Sarris' "The American Cinema: Directors And Directions, 1929-1968".

If you don't, you need it. Real bad.

I also would recommend Sarris' "Confessions Of A Cultist: On The Cinema, 1955/1969"

And I highly recommend Robin Wood's book-length study of the films of Howard Hawks called "Howard Hawks".

And also Wood's "Hollywood From Vietnam To Reagan. . . And Beyond."

These are all very interesting.