I can't believe that I missed this announcement, especially after seeing in in action back at GameFest...Firelight Technnologies has released FMOD Ex (aka FMOD 4).
Personally, I think it's an amazing set of audio libraries. On the managed front, it now ships with official managed interfaces (VB.NET/C#). The library has been restructured completely to make it even easier to use. The FMOD Designer tool is a dream, and the CPU usage is incredibly small, even on the Xbox 360.
So if you're looking for a great affordable library for your commercial product, or a free sound library for your personal use, go check it out.