Hardwipe is a free file wiper and drive cleaner for Windows.
It can be used to permanently erase, or to "hard wipe", data on disk and portable storage media (i.e. USB flash-drives) to prevent personal and sensitive business information from ever being recovered. It can wipe entire drives, wipe files individually, and sanitize unused drive space. It runs from within the OS, and supports right-click context menus in Windows Explorer, or can just be used as a standalone application.