Disk Sorter (Freeware)

DiskSorter is a file classification solution allowing one to classify files in local disks, network shares, NAS devices and enterprise storage systems. Users are provided with the ability to gain an in-depth visibility into which types of files are using most of the disk space, save reports and perform file management operations on categories of files.

They've got a Freeware version on the site.

http://www.disksorter.com/downloads.html