Performance Tuning: The performance counters below are very helpfull in diagnosing issues with SQL Server. They are classified into groups to better understand the usage. There are many articles already on Internet on these counters but this will be my way of representation.
Operating System Memory Counters
OS Memory and Paging Performance Counters
OS Disk and Miscellaneous Counters
SQL Server Memory
Buffer Manager & Memory Performance Counters
SQL Server: Memory Manager Counters
My Memory Usage– Performance Counters
Other Important Performance Counters
Data Access Performance Counters
User Database Performance Counters
SQL Server SQL Statistics Counters
Important Perfmon Counters %Processor and Disk monitoring counters
SQL Server : Plan Cache Counters
Users & Locks Performance Counters
Another way to Access perfmon data
Getting Perfmon data from inside of SSMS