This app forces the Android Media Scanner to run.
I do this whenever I see duplicates in the music list, or when I manually add and media to the device over USB.
It works with the newer phones including 4.0 ICS/Ice Cream Sandwich and 4.1 JB/Jelly bean, and now 4.2.
To test the media scanner or to clean out the media cache:
Go to settings.
Click All Applications tab.
Click Media Storage.
Click Clear Data.
Now run Force Media Scanner and click the Scan button.
It will take a long time the first time you do this, as it has to read and process each video, and music file on the device.
Afterwards, runs will be much faster, and it's just updating the media store.
It's new, so if you have any issues, please email me.