Duel Madness is a theme in Yu-Gi-Oh with a heavy techno feel to it; this, combined with it being played frequently while Seto Kaiba is onscreen, has led it to become somewhat of an "unofficial theme" for Kaiba among fans. A vocal version was released on the CD Yu-Gi-Oh! Music to Duel By, but the instrumental version was not.
Joel Douek, one of the composers of the series' themes, has recently begun releasing many of the previously unreleased themes, among them is the TV version of "Duel Madness" (called "Kaiba - Hacker"), and an instrumental version of Duel Madness.
These are fan-made AMVs.