Maybe it's just that nobody around here is an expert. He asked for a
good one. There are in fact loads of such programs. For converting MP3s to WAVs, I've got the shareware version of AudioEdit Deluxe and the freeware CoolDecode. How they measure up to others around isn't really known to me. They do their job. Even Windows' Sound Recorder utility allows you to switch between various WAV formats.
You might want to check some of these lists out at Tucows:
http://www.tucows.com/audiocon95_default.html
http://www.tucows.com/audioedit95_default.html
Some game developers store sounds in their own proprietary formats. In this case you'll need a fan-made ripper utility (if one exists) to extract the goodies first.
Edit: Too late, I guess.