(* Source: Mark Heffliger *) 

Apple announced on Tuesday that its iTunes Store is now the second-largest music retailer in the U.S. behind Wal-Mart, having leapfrogged retail chain Best Buy in the latest figures from market research firm NPD Group. The company pulled ahead of then third-place U.S. music retailer Amazon.com last June, according to NPD's rankings.

Apple also announced that there are now over 50 million iTunes Store customers, and that the company has now sold over four billion songs -- including 20 million sold on Christmas Day 2007 alone.

"We'd like to thank the over 50 million music lovers who have helped the iTunes Store reach this incredible milestone," said Eddy Cue, Apple's vice president of iTunes.