I am a firm believer that a very significant piece of learning, particularly in the IT field, is reading a great technical book pertaining to your profession and desires (in my case, SQL Server and Data in general).  Listed below are books that I have found extremely useful, and are within arm's reach at all times:

Microsoft SQL Server 2012 Administration
Authors: Adam Jorgensen, Steven Wort, Ross LoForte, Brian Knight
Description: A great book on SQL Server 2012 for the DBA.  A lot of cumulative information for past versions, as well as new additions to SQL Server 2012.

Microsoft SQL Server 2008 Administration with Windows PowerShell
Authors: Ananthakumar Muthusamy, Yan Pan
Description: This book is perfect for the PoSh beginner and advanced  audience.  It has a focus on implementation for SQL Server, and is a great place to start for automating SQL Server.

SQL Server 2008 Internals and Troubleshooting
Authors: Christian Bolton, Justin Langford, Brent Ozar, James Rowland-Jones, Steven Wort
Description:An excellent book on a lot of the internal workings of the database engine, and then finishing up the book with great troubleshooting strategies.  I highly recommend this book for any SQL Server professional looking to expand their knowledge.

Microsoft SQL Server 2008 Bible
Authors: Paul Nielsen, with Mike White and Uttam Parui
Description: If there is one book that touches upon everything that can possibly be talked about within SQL Server in one book, it's this one.  Very daunting with over 1600 pages, but with a little patience and a great reading schedule, time will fly by emersed in these informative pages.

Microsoft SQL Server 2008 R2 Unleashed
Authors: Ray Rankins, Paul Bertucci, Chris Gallelli, Alex T. Silverstein
Description: A very good and in-depth reference book, and one of the very few on 2008 R2!

Microsoft SQL Server 2008 Management and Administration
Authors: Ross Mistry, with Hilary Cotter
Description: Another great reference book, very straightforward and to the point during those hectic times when you just need to get something setup.

If you have any particular favorites, please let me know!  I'm always in the market for a new SQL Server book (and believe me, my wish-list is already chock full), and I'd love to hear about it.