The February 2011 release of the Xbox 360 XDK includes a new version of XNA Math, version 2.04. We are making it available here for Windows developers. The update is subject to the same EULA as the DirectX SDK (June 2010) release.
XNA Math version 2.04 includes:
Update: There is a newer revision of this math library available as part of the Windows 8.0 SDK and Visual Studio 11 Beta known as "DirectXMath". You can think of it as "XNAMath version 3.x". It is very similiar although it does have a number of 'breaking' changes (there's a migration guide as well), requires Visual Studio 2010 or later, and is not available for the Xbox 360. If you need to maintain compatibility with the Xbox 360 version in the XDK or VS 2008, you should continue to use XNAMath version 2.x.