Itzik's books are some of the first I recommend. After that, get a copy of Kalen Delaney's book SQL Server Internals. Since you're just getting going, you might want to check out a book I wrote a few chapters for, Beginning SQL Server 2008 Administration. It has a lot of basic guidance for getting things set up. After that, you start to get into specialty books and it really depends on what you're looking to do with your time and your career.