There are multiple tools and plugins available for .net application logging, based on its license, easy to use, easy pluggable, least impact on performance and best fit into .net environment, below are the tools listed on priority wise.
ELMAH (Error Logging Modules and Handlers) is an application-wide error logging facility that is completely pluggable.
The Apache log4net library is a tool to help the programmer output log statements to a variety of output targets. Log4net is a port of the excellent Apache log4j framework to the Microsoft.NET run time.
Microsoft Enterprise Library
Logging Application Block. Developers can use this application block to include logging functionality for a wide range of logging targets in their applications. This release adds asynchronous logging capabilities.
Rich Logging & Tracing Track messages, errors, objects, database results & more. Logging support to any .NET desktop application, ASP.NET server project or multi-tier database solution.