FMOD is one of the best out there. SDL has a sound component iirc, and there's openAL. And DirectSound is still viable I think. I am not sure; I use FMOD and love it.

I second FMOD. It's cross-platform, it's got nice API with good documentation, and has high-level features (like loading an mp3 and playing) as well as low-level DSP stuff if you need to use it. The designer app is pretty nice too if you take the time to learn it.

My take on the other available API's...

SDL w/ SDL_mixer: very easy to set up and use. If all you want to is play sounds and play/loop some music, it will do the job.

OpenAL: low-level, C API. Has some issues due to there being no ARB to regulate new versions. Only API that will give you hardware acceleration on Vista (if their sound card has an OpenAL driver).

DirectSound: never used it myself. From what I gather it's also very low-level like OpenAL. Gives you hardware acceleration in XP and previous versions of Windows.

Use FMOD Ex, it's the latest version and has full support for Vista x64 as well as the new Vista WASAPI interface. Plus if you're using C++ the FMOD Ex has an object-oriented wrapper for the main API.