Understanding Performance Counters data while troubleshooting Performance issues in SQL Server: http://blogs.technet.com/vipulshah/archive/2006/11/30/understanding-perfmon-counters-while-troubleshooting-sql-server-performance-issues.aspx

External Links:

http://www.extremeexperts.com/SQL/Articles/SQLCounters.aspx

http://www.sqlservercentral.com/articles/Administering/performancemonitoringbasiccounters/1348/

User Settable queries:

http://searchsqlserver.techtarget.com/generic/0,295582,sid87_gci1110440_tax301334,00.html?adg=301324&bucket=REF#