http://www.youtube.com/watch?v=gs9Xxc-_a6o
Pluck is a recently released tweak that places a dedicated button on the iPhone's Lock screen for selecting Music. To view the button, simply invoke the iPhone's music controls by double pressing the Home button while on the Lock screen. Tapping the button allows you to "pluck" a new track from your Music Library, instead of forcing you to unlock the device and venture into the Music app just to select a specific song.
Once the button is tapped, a new sheet featuring your Music Library is pulled in from the bottom of the screen. This sheet can also be accessed by means of an Activator gesture, which is configurable in Pluck's preferences. Check inside for a few more details.