Apple today announced that more than five billion songs have been purchased and downloaded from its iTunes Store since its debut five years ago. The digital download service is currently the number one music retailer in the US, according to the most recent data from market researcher NPD, and features the largest music catalog with over eight million songs.

Music buying has certainly been migrating online over the past few years, with CD sales declining steadily as more consumers switch to digital media players. Apparently, the same is starting to become true for video – albeit in a much smaller fashion – with the DVD business posting its first year-over-year sales decline in 2007 since the format’s rise a decade ago. Apple of course is capitalizing on this and has revealed that customers are buying and renting over 50,000 movies every day, making iTunes the most popular online movie store as well.