I've always loved the music from this game, specifically the music from the "History Video" from the main menu in the PS1 version,"R U Ready", and "Cold Fusion Power" from the GBA version's main menu, and "The Moebius" from in-game races in the PC version.
all of these songs are by Morphadron(a.k.a. Romolo Di Prisco or Rom Di Prisco), and i have all 3 if anyone wants them to work from. all 3 songs can also be found on beemp3.com, and can be found just by searching "Morphadron".