This topic provides a list of performance counters you can find in the Performance Monitor.
Often times, it is not trivial to define a comprehensive set of performance counters upfront. Continuous investigation and improvement are the way to go. It is a good idea to leave these counters on after development is finished, because your application will not live in a vacuum; there are tons of things which may impact performance, and thus your custom counters will do a great job for maintenance and on-going monitoring.
The nicest thing about performance counters is that they enable you to easily monitor your own application-specific and business-centric counters against the built in counters, such as those that relate to GC, Exceptions, Threading, etc, and they give you all this rich information with only a minimal impact on your application.