New York - Viacom's (NYSE: VIA) Harmonix Music Systems, a unit of MTV Games, announced on Friday that gamers have purchased more than 2.5 million downloadable song packs for the music-based game since its launch on Nov. 20. The top-selling song pack features three songs from Metallica, followed by packs from The Police, Queens of the Stone Age and David Bowie. Pricing is $0.99 to $2.99 per track, with the majority sold for $1.99. "The incredible response to the downloadable content we've released to date motivates us even more to establish this platform as a way for people to discover new, up and coming artists through the game -- in addition to delivering great game play experiences set to the music of mega-artists," said MTVN Music Group/Logo/Films president Van Toffler.