Execution Plan
Understanding SQL Server Execution Plan
An execution plan explains the processing approach (including multiple intermediate steps) used by the query optimizer to execute a query. Below are the best resources you could get to understand the SQL Server Execution Plan.
SQL Tuning Tutorial - Understanding a Database Execution Plan (1)
Codeproject
Execution Plan Basics
Simple Talk
SQL Server Execution Plans
SQL Server Central
SQL Server Query Execution Plan Analysis
SQL Server Performance
Sql Server Actual Execution Plan Vs Estimated Execution Plan
SQL Authority
Understanding Microsoft SQL Server Execution Plans
Channel9