Apple has started variable pricing for the music found in iTunes Store. Announced back in January at Macworld 2009, popular tunes are priced at US$1.29 while others are priced at US$0.99 or US$0.69. Songs within an album can also have variable pricing.
Take for example, Lady Gaga’s album “The Flame”:http://itunes.apple.com/WebObjects/MZStore.woa/wa/viewAlbum?id=294084085&s=143441, some of the popular tunes are priced at US$1.29 while others are priced at US$0.99. However, the album still sells at US$9.99.