I feel like I am cheating on my wife. I’m listening to music downloaded from the new Amazon MP3 store — in iTunes and on my iPod.

Years ago, before the iTunes Music Store, I dreamed of a time when I could download music from any online store and play it on any digital music player. Online music stores were rare then, but then Apple opened the iTMS in April 2003 and downloading legal music took off.

At the time, I was forced to deal with digital rights management (DRM) that said I could only listen to iTunes music on an iPod. Apple offered the best digital music players and a pleasant online music store experience, so I turned to Apple, the iPod, iTunes, the iTMS, and simply endured DRM.

Even so, I’ve always wanted my music DRM-free, so I could use it on different devices, and share it with my daughter and wife. Apple said no, I can’t do that, so the music in the family remains crippled, tied to different user accounts, and a pain to share.

That all may change now that Amazon has opened its DRM-free music store, Amazon MP3, which offers a stout 1-2-3 combination for music downloads. Now I can purchase music and listen to it on any PC, Mac, or Linux computer using iTunes or almost any media player software. Better yet, I can listen to the songs on any digital audio player — an iPod, one of the Creative Zens, a Zune — and I can share them with the wife and kid.

My dream has come true.

Update: see our full Amazon MP3 review.

The iTunes Music Store has fended off all comers to remain the top digital music store in the world. Now Amazon, with its just-opened MP3 store, aims to knock iTunes off its lofty perch and in doing so may change the future of digital music downloads.

Amazon today opened Amazon MP3, its much anticipated storefront for selling music downloads free of digital rights management (DRM). As expected the service utilizes the ubiquitous mp3 format, meaning that music downloaded can be played on any — yes, any — device that supports mp3s, including Apple’s iPod and iPhone, Microsoft’s Zune, and the Creative Zen series of players, as well as most modern cell phones. Although Amazon MP3’s download manager is Mac and Windows-only, so Linux fans are out of luck (Update: Amazon says a Linux version is in the works).

It’s a gamble we all take when we sign up for a digital music service: Will it still be around in a year or two?

The latest digital music store to go belly up is Virgin Digital, which its owner, Virgin, is in the process of shutting down in the US and UK. Once the store goes dark Oct. 19, customers will not be able to play their songs due to digital rights management (DRM) limitations.

Rest at ease, iTunes. SpiralFrog is no prince.

SpiralFrog is an ad-supported free-music download site that launched today after nearly five years of development and a year of beta testing. It boasts 800,000 songs and 3,500 videos available for download … free of charge.

The catch, of course, is that you must view advertising in order to download DRM-protected music and video. SpiralFrog is built on a revenue-sharing agreement with participating labels, and your eyeballs pay for the music.

In addition to viewing ads while searching for and downloading music, SpiralFrog requires you to log in to the site and view ads at least once every 30 days, or the downloaded music for the account becomes disabled.

Tracks from SpiralFrog also cannot be burned to a CD or transfered to an iPod, the top-selling digital music player, although files can be sent to two Windows Media Player-compatible devices or cell phones. (FAQ.)

While getting free music is compelling, I doubt SpiralFrog will knock the iTunes Music Store off its perch because, at least for me, the site was frustratingly slow (chalk this up to a lot of interest on launch day) and the interface to browse and download made me feel like I was querying a database and not thumbing through a digital record bin like iTunes.