This is a completely unconfirmed rumour for now, but it seems like someone with ties to Microsoft claims the Xbox 360 will get a music store of its very own. The process will be similar to the subscription model the Zune has, which is $15 a month to have access to the entire library of tracks on the Zune marketplace for renting/streaming.
What's the Zune connection? Well, it would be likely that if you've already got the subscription model on your Zune that Microsoft won't charge you twice for access to the same tracks. This could be a big tie-in to help Zune sales and increase content for the Xbox 360 at the same time. A very interesting rumour that we're going to be keeping our peepers on.