DriveGauge

DriveGauge is a simple yet powerful, fully customizable utility designed to provide visual feedback about how full your drives are directly on each drive's icon.

Launch DriveGauge and it will automatically build and then update a Drive List containing a list of all your currently mounted drives and relevant information about them. It only requires a click on the drive's icon in the Finder to see its updated look. A quick and painless way to keep tabs on your drives.