Amazon has introduced a new service, where if you buy a physical CD, a digital version will become available to you too. The company calls the new service 'AutoRip' and it's not only available for new CDs you purchase. The company states on its website that MP3 versions of tracks from CDs purchased from Amazon since 1998 will also be available, if they are eligble for AutoRip that is. To find out which CDs are eligible you can search the Amazon website for CDs that feature the AutoRip logo or check this page.
The MP3 versions become available from the Amazon Cloud Player which also allows you to stream the music on your computer and mobile devices. And if you purchase a CD, you don't have to wait with listening to the music you've purchased, the MP3 versions are directly available from the Cloud Player. Currently the service is only available for customers in the United States and there is no word if and when it will become available to others users around the world.