.NET - how to play sound files?

What is the best class/assembly in .NET 4.0 to play audio sounds in an application? Ideally, I would like to do this in a multithreaded way so that I could feasibly play two sounds simultaneously and/or in a loop.

Thanks.

Microsofts NAudio Lib should fit in most szenarios.

The waveOut API is less complex and support simultaneous playback too.