With iOS 6, you can roll out of bed to a mellow reggae beat or leap out of bed to thrash metal -- your choice.
If you use your iPhone as your alarm, you likely have grown tired of starting your day to the same marimba tone. You may not have noticed yet that after you can set the alarm to play a song instead of a tone.
Open the Clock app and choose Alarm. When you add a new alarm or edit an existing alarm, tap Sound. Here, you'll see a new Songs section. Tap "Pick a song" and you'll see a list of the songs in your music library. Choose a song and that's what you'll hear to start your day or end your nap.
If you use iTunes Match and have it set to display both locally stored songs and those in iCloud (Settings > Music > Show All Music), you can choose a song from iCloud as your alarm. Be careful, however, with choosing a song from the cloud -- if you lose Internet connectivity while sleeping, your alarm will be silent. I tested this by selecting a song that I hadn't downloaded to my iPhone, set the alarm, and turned on Airplane mode. When the alarm went off, it was silent. A best practice here would be to download a song to your phone before using it as your alarm.
This new feature is available on the updated Clock app for the iPhone and the new Clock app for the iPad.
For more on Apple's new mobile operating system, check out our complete guide to iOS 6.