MPQ Editor
MPQ (MoPaQ) is an archive format developed by Blizzard Entertainment, purposed for storing data files, images, sounds, music and videos for their games. The name MoPaQ comes from the author of the format, Mike O'Brien (Mike O'brien PaCK). So far, MPQ archives have been used for the following games:
Diablo
StarCraft
Warcraft II (Battle.net Edition)
Diablo II
Warcraft III
World of Warcraft
Starcraft II
Lord of Magic (by Sierra)
Hellfire (Diablo datadisk by Sierra)
http://www.zezula.net/en/mpq/main.html
http://www.zezula.net/en/mpq/download.html
Besides MPQ Editor, there are more utilities to be helpful for developers. Against a broken link, I attached (currently) the newest versions including StormLib library.