Apple Computer strengthened its grip on the digital media market this week, adding three major media sources to its list of iTunes content providers.

Warner Brothers, E! Entertainment, and Metallica have all agreed to provide select content to the iTunes Music Store, Apple's online market selling music and video's for download. The store currently includes over 9000 music videos and short films, including features from Pixar and Disney.

On Tuesday Warner Brothers made a number of its classic television programming available for purchase and download. Warner Brothers opened up their vaults making programs like Friends, Babylon 5, available, as well as animated classics including The Jetsons and The Flintstones.

Warner Brothers said it was a first step towards making its content available digitally, and that the deal fits perfectly with their philosophy, according to Simon Kenny, president, Warner Bros. Digital Distribution.

E! Entertainment followed suit on Thursday, making episodes of its The Simple Life series available and The Soup. Users will also be able to get a behind-the-scenes look into the Playboy Mansion life in The Girls Next Door.

The shows are available in the US only and follow the traditional $1.99 per episode pricing scheme.

On top of these new streams of content, the most notable act to join iTunes is the addition of metal-rock group, Metallica.

Since the creation of peer-to-peer network Napster - which allowed users to swap music free of charge - the band has been adverse to joining digital music wave.

At the time, a member of the band, Lars Ulrich, collected 300,000 names of Napster users that had downloaded Metallica tracks and handed them over to the courts - a defining image of the early days of digital music.

Their perspective has since quelled, and given the secure, revenue based nature of iTunes, they have decided to join.

iTunes now offers all the songs from the bands first four albums, Kill em all, Ride the Lightning, Master of Puppets and And Justice for All.

Fans may buy tracks a la carte for 99 cents or purchase the albums, starting at $9.90.