Crazy Media Converter is a free portable converter developed to convert less popular audio formats such as, Ogg, Acc, Wma, etc into more popular Mp3 format.
Update: I would highly recommend giving FanVista Audio Converter a try. It is a free advanced audio converter and extractor.
The developer calms that one can convert any format into any other custom-specified format, but it failed to convert Avi to Mp3, Flv to Avi, Flv to Mp3, and so on during my testing. Further tests revealed that it can best be used to convert Ogg, Acc, Wma to Mp3 audio format only.
Just drag the media file and drop it to the Crazy Media Converter floating icon.
This will open a new window with your media file added to the list. You can add multiple media files for batch conversion.
Once all media files have been added, hit the Convert button. After conversion is complete, the output directory will open as a new window from where you can access your newly converted mp3 audio files.
It works on all versions of Windows. Enjoy!