I owe a great deal to the kind folks who answer questions and write articles for SSC, and other sites too. I also owe a lot to the people that post their questions because they provide real-world problems for me to research and resolve, which has proven to be an exceptional way to learn. Personally I think book-reading and staying active online complement each other quite well. If you're into T-SQL development I would recommend anything written by Itzik Ben-Gan:

Amazon > Books › "Itzik Ben-Gan"

This one if you're just getting started and want to stay in front of the newest version...or have been at it a while but want a formal comprehensive walk-through to fill in any holes in your knowledge you suspect you may have:

Microsoft SQL Server 2012 T-SQL Fundamentals by Itzik Ben-Gan