I work with a motley crowd of developers and have the opportunity to give lunch and learn training sessions on SQL Development.
Most recently, I put together a .zip file of T-SQL scripts that developers would find handy. You can download it here.
Here's a summary:
Missing Indexes - missing indexes.sql, missing index setup demo.sql - more about this here
Index Usage - index usage.sql
Sessions and Requests - sessions and requests.sql - more about this here
Most expensive queries - worst queries.sql - from MS PSS
Tables without clustered indexes - tables without clustered indexes.sql
Deadlocks XEvents - deadlocks in xevents.sql - more about this here
Dependencies - dependencies.sql - more about this here
Stored Proc Execution plans - cached exec plans.sql - more about this here
Volume Stats - volume stats.sql
Modules vs. Routines - modules vs routines.sql - more about this here
EDIT: 10/17/2013 refreshed the toolbox.zip file with latest updates from my personal toolbox.