The latest NPD figures on music sales are out for the first half of 2008 and, to no one’s surprise, Apple’s iTunes Store continues to be the dominant force. The NPD data takes into account purchases of physical CDs, digital music, as well as over-the-air wireless transactions – but not subscription-based online services.

This further confirms that Apple’s achievement of surpassing music sales at Wal-Mart earlier this year wasn’t just a one-time blip but rather a trend. Retail giants Wal-Mart and Best Buy are still following Apple in second and third respectively, with the only notable shift in the top-five placement corresponding to Amazon.

The online-only vendor rose from fifth to fourth based upon a combination of its online CD sales and the launch of its digital music store last year. If anything, this could be seen as an indicator that the company may eventually challenge iTunes’ top position given its somewhat broader consumer base – though Apple will likely keep that title for some time.