Windows Media Lossless
Windows Media Audio Lossless, or WMA9 Lossless, is the best of all Windows Media Audio codecs in terms of audio quality. As with any other lossless compression format, it produces a 100% copy of the original audio file so that no data is lost. Microsoft gears the codec toward uses for archiving content masters and so on.
Microsoft estimates that the Windows Media Audio 9 Lossless Codec can compress at a 2:1 or 3:1 ratio. This would depend on the original content. Unlike MP3, this codec and other lossless codecs, cannot discriminate much between data. MP3 and other lossy formats literally cut data permanently from the original source of the audio, which is why they can achieve such a great compression ratio (4MB decent quality full length tracks for example). With the lossless WMA codec, all of the original data must be kept intact, just compressed. You could compare this to storing an executable file in a ZIP file; you cannot lose any of the data or else you won't be able to run it afterwards.
The Windows Media Audio 9 Lossless codec also offers dynamic range control using the maximum and average audio amplitudes that are calculated during the encoding process. Using the Quiet Mode feature in Windows Media Player 9 and later, users can hear the full dynamic range, a medium difference range up to 12 dB above the average, or a little difference range up to 6 dB above the average.
A free and widely used lossless audio compression format is Free Lossless Audio Codec (FLAC).