Music Unlimited is part of the Sony Entertainment Network and offers 18 million songs, though not all of them are available everywhere due to the usual rights issues.
Subscribers listening to the music on Windows or OS X based computers, Android smartphones or tablets, the Sony Android Walkman or the PlayStation 3 are now able to select high quality streaming to receive 320kbps AAC streams.
That should give an appreciable improvement over the default 48kbps HE-AAC stream, particularly when listening via home entertainment gear. But it does come at a significant cost in terms of data usage, so it's probably best to stick to the default on your smartphone or tablet.
Subscriptions cost $7.99 per month (Mac, Windows and PS3 only) or $12.99 for premium access via any supported device. A 14-day free trial is offered.