I hope this isn't too off-topic, but the best system administration book I've ever read is "The Practice of System and Network Administration" by Limoncelli and Hogan.
It doesn't cover the specifics of any particular technology, it covers the processes. It is at a higher level than day to day administration and covers bigger topics. There are tons of real world examples taken from the author's job experience. And every chapter includes a checklist type summary of things from the chapter that you should look at in your own environment.
The kind of topics it addresses are how do you design a service for performance and stability, how do you upgrade applications or services with minimum user impact, what strategies work best for handling network growth - stuff like that. There are even chapters on hiring and firing system administrators, how to handle your non-technical managers, tips for increasing job satisfaction, and so on.
While this certainly won't help you with your certification, it is fantastic at teaching you the kind of thing a senior admin or architect has to think about. When I went from the most junior member of an 8 person admin team to my next job as the more senior of just 2, it was invaluable in helping me adjust my thinking so I could see the big picture of what I had to do to manage my new Unix environment.
