Apple today kicked off its countdown to half a billion songs sold on the iTunes Music Store with an online song counter “so music fans around the world can participate in the race to purchase and download the 500 millionth song.” As part of the countdown, Apple is giving away an iPod mini and an iTunes gift card for 50 songs to the iTunes customer who purchases the winning song at each 100,000 interval. The person who downloads the 500 millionth song will win the grand prize — 10 iPods of their choice to share with family and friends, an iTunes gift card for 10,000 songs and an all-expenses paid trip for four to see Coldplay on their world tour.