There are many publications that are now available about video game music and sound design.
The UK Video Game Music Research group keeps a list of some academic research published in the area of game music/sound.
Dr. Mark Grimshaw likewise keeps a bibliography of research relating to game sound.
Playing with Sound: A Theory of Interacting with Sound and Music in Video Games by Karen Collins
Sound Play: Video Games and the Musical Imagination by William Cheng
Playing Along: Digital Games, YouTube, and Virtual Performance by Kiri Miller
Oxford Handbook of Interactive Audio by Karen Collins, Bill Kapralos and Holly Tessler (eds).
Music In Video Games: Studying Play by K.J. Donnelly, William Gibbons and Neil Lerner (eds).
Music and Game: Perspectives on a Popular Alliance by Peter Moormann (ed.)
Game Sound Technology and Player Interaction: Concepts and Developments by Mark Grimshaw (ed).
Computer- Und Videospielemusik Im Musikunterricht (German Edition) by Sebastian Wolf
From the Shadows of Film Sound: Cinematic Production & Creative Process in Video Game Audio by Rob Bridgett
A Composer's Guide to Game Music by Winifred Phillips
From Pac-Man to Pop Music by Karen Collins (ed.)
Game Audio Culture by Rob Bridgett
The Game Audio Tutorial: A Practical Guide to Sound and Music for Interactive Games by Richard Stevens and Dave Raybould
The Essential Guide to Game Audio: The Theory and Practice of Sound for Games by Steve Horowitz and Scott Looney
Writing Interactive Music for Video Games: A Composer's Guide by Michael Sweet
Game Music Online
Mix Online game audio magazine
Gamasutra, regular articles on game audio
FilmSound articles, also links to game articles
Video Game Music Nerd
Kotaku gamer mag online
Kill Screen well-written journalism about games