irrKlang is a cross platform sound library for C++, C# and all .NET languages
http://www.ambiera.com/irrklang/
It is a high level 2D and 3D cross platform (Windows, Mac OS X, Linux) sound engine and audio library which plays WAV, MP3, OGG, FLAC, MOD, XM, IT, S3M and more file formats, and is usable in C++ and all .NET languages (C#, VisualBasic.NET, etc).
BASS is an audio library for use in Windows and Mac OSX software. Its purpose is to provide developers with powerful and efficient sample, stream (MP3, MP2, MP1, OGG, WAV, AIFF, custom generated, and more via add-ons), MOD music (XM, IT, S3M, MOD, MTM, UMX), MO3 music (MP3/OGG compressed MODs), and recording functions. All in a tiny DLL, under 100KB* in size.
http://www.un4seen.com/
On Windows, BASS requires DirectX 3 or above for output, and takes advantage of DirectSound and DirectSound3D hardware accelerated drivers, when available. On OSX, BASS uses CoreAudio for output, and OSX 10.3 or above is recommended. Both PowerPC and Intel Macs are supported.