Apple's iTunes allows you to purchase songs online for just $0.99. The company has already sold more than 430 million songs worldwide and last week they announced that they have sold their 50 millionth song in Europe. More than 1.5 million songs are currently available on iTunes.
However, competitors such as Napster, Real and Yahoo are trying to penetrate the online music market by offering new subscription online music stores that allow you to download an unlimited amount of songs for a monthly fee.
iTunes 4.9 can be downloaded here