I have also heard good things about NLog although I haven't tested yet. They say the API is similar to the one provided by log4net.
Also, looking through SO you have a lot of questions related with this issue:
https://stackoverflow.com/questions/98080/what-is-the-best-logging-solution-for-a-c-net-3-5-project
.NET logging framework
Error logging in C#
Hope this helps.