Modern immunology textbooks
I am surprised Janeway's Immunobiology is not listed here:

Murphy K. Janeway's Immunobiology. 8th ed. New York: Garland Science; 2011.

It is very comprehensive, accessible and goes beyond any graduate course I know. Most immunology researchers I know have a copy of this handy somewhere in their office. A particular highlight are the very clear illustration.

I would suspect that a new edition is currently in the works, so I recommend checking if a new edition is due to come out before you buy.