Forcing a Parallel Query Execution Plan by Paul White. This includes references on what can make a plan, or a zone in a plan, remain serial.
Fixing a Filtered Index which is Causing Data Modifications to Fail by Kendra Little
Link to Microsoft’s reference: Required SET Options for Filtered Indexes
A plan explanation involving Lazy Spool by Hugo Kornelis
An explanation of Eager Spool by Fabiano Amorim
That’s Actually a Duplicate Index by Jason Strate
Latest publications by Louis Davidson on Relational Database Design
SQLChallenge focusing on tuning TSQL using windowing functions - Speed Up the Popular Names Query