Microsoft's DirectX Software Development Kit
The home of Ogg Vorbis
An audio library. The license is free for non-commercial products, but could be a bit pricy for shareware products.
SFML - Simple and Fast Multimedia Library
zlib open source, cross platform, light-weight library for doing various low and high level tasks: windowing, audio, input, networking, graphics, etc. SDK is based on separate classes so it's possible to use parts of the library if that's what's desired.