Over the last decade, iTunes has become not just the world's biggest music retailer, but also one of the best. There's not much that you can't find in its massive repository of digital music, movies, apps and podcasts. It also interfaces well with Apple's mobile devices and PC's, leaving users with very little need to try alternatives.

But there are some relatively new services available that provide a different experience for avid music listeners that some may find useful, particularly for those who have an insatiable thirst for finding bands and artists they've never encountered, or for people who want to try out an album before purchasing it.

We'd like to outline some of these services, which offer both paid and free options:

• Spotify -- This is one of the most popular music subscription services available, with 20 million active users and 5 million paid users worldwide. The basic service lets you stream virtually any song or album you want from the a collection of 15 million songs, with paid advertisements playing about every ten minutes. Subscribers who pay a monthly fee of $9.99 can listen without having to deal with marketing materials, and have the ability to download an app to their mobile devices so that they can enjoy the music anywhere. It's like having your own personal library of 15 million songs.
• Rdio -- This service is similar to Spotify, with free (advertising-supported) and paid subscription plans, and a massive library of millions of tunes. But the interface is a little bit cleaner, with less focus on recommending music. This may be preferable for users who know what they want. Another great feature of Rdio is its selection of expertly-curated internet radio stations, which provide a great way to learn about new artists and songs.

The paid versions of both of these programs will let you stream to a mobile device such as an Apple iPad mini or iPad 4, so head on over to the PortableOne online store for our latest deals on Apple tablets.