This is the music you hear during the Conveyor Belt levels as well as a few mini-games.
I originally composed "Ultimate Battle" for the boss battle music in my indie rpg "Melolune." But after George heard it, he asked if he could use it in Plants vs. Zombies... I said that was fine as long as I still had permission to keep it as the boss battle music in my game. So if you ever play Melolune and hear this music, that's why :P