I'd recommend the Microsoft Enterprise Library which contains the Logging Application block. I've been using it for some time and it works well.
http://www.codeplex.com/entlib/Release/ProjectReleases.aspx?ReleaseId=4474
I use it in WebApps to write out to the Virtual Directory. It's fairly granular and you can easily customise it for your own application
This http://www.codeproject.com/KB/architecture/GetLoggingWithEntLib.aspx is a good article about using it