I was a DBA turned developer in 2010. I like administration but love development. If you are interested in a career as a SQL Developer you should consider getting up to speed on SSIS. It seams that most SQL Developer jobs these days require some SSIS experience. You don't have to be a guru but some experience will certainly make you competitive.

Microsoft SQL Server 2012 High-Performance T-SQL Using Window Functions by Ben Gan is my favorite T-SQL book and covers some common real world problems in an effective way.

These can be downloaded for free from Redgate Press:

Inside the SQL Server Query Optimizer by Benjamin Nevarez

SQL Server Execution Plans by Grant Fritchey

Both are great.

Any blog post by Jeff Moden, Dwain Camps, Paul White, Adam Mechanic, Gail Shaw or (of course) Ben Gan is worth the read.

SQL Server Central stairways are great too.