As you would expect, the world's tallest fountain is in Dubai. As you would expect, it's next to the world's tallest building. And as you would expect, it's as naff as everything else in there.
The Dubai Fountain—which was recently finished by the Burj Dubai—can reach 492 feet up in the air.
It was built for $217 million by WET Design, which is the same company that created the one at the Bellagio Hotel, in Las Vegas. The 900-foot long water show uses 6,600 lights, 50 colored projectors, and hundreds of servos, all computer controlled and synchronized with music to offer some of the most sophisticated water entertainment since Zeus decided to impregnate Danaë. [Wikipedia and Dark Roasted Blend]