Apple’s digital music store has topped again the US music retailers. According to the latest results released by The NPD Group, the company that tracks the music sales in the United State, Apple’s iTunes is leading the pack in the first half of this year.

Apple’s achievement is remarkable because unlike its main competitors, Wal-Mart and Best Buy, iTunes sells only music to download, while the other two are also offering music in CD format. Earlier this year, Apple surpassed Wal-Mart in terms of sales for the first time.

The study released by The NPD Group brought also good news for Amazon.com, the biggest online retailer. Amazon.com reached the fourth place, one step higher than its previous place.

Apparently, Amazon’s effort with Amazon MP3 has started to pay off and on the other hand the online CD sales have seen less erosion than CD sales at brick-and-mortar stores.

However, The NPD Group predicted that Apple would maintain its lead, because CD sales are going at a slow pace, with most of the people changing their buying habits toward digital stores.

Last month, Apple announced that the sales of its iTunes online music store have gone past the five billion mark. iTunes was launched about five years ago and during this time, it has had a phenomenal evolution: more than 50 million customers totalling five billion songs.

1. iTunes
2. Wal-Mart (Walmart, Walmart.com, Walmart Music Downloads)
3. Best Buy (Best Buy, Bestbuy.com, Best Buy Digital Music Store)
4. Amazon (Amazon.com, AmazonMP3.com)
5. Target (Target and Target.com)