What tag types could be interesting:

o  ID3v1
o  ID3v2: http://www.id3.org/Developer_Information
o  Lyrics3: http://www.id3.org/Lyrics3
o  Lyrics3v2: http://www.id3.org/Lyrics3v2
o  APE: http://wiki.hydrogenaudio.org/index.php?title=APE_Tags_Header

Headers:

o  Xing: http://www.codeproject.com/audio/MPEGAudioInfo.asp
o  LAME: http://gabriel.mp3-tech.org/mp3infotag.html
o  VBR: http://www.iis.fraunhofer.de/fhg/iis/EN/bf/amm/download/sw/index.jsp

Test suites:

o  http://www.getid3.org/demo/

Other utilities:

o  http://mp3gain.sourceforge.net/
