Files deleted by the Macintosh through the trash can are easily recovered using most disk utilities, including Norton and MacTools. Burn securely erases data in sensitive files by overwritting the data one or more times before the file is deleted. When combined with encryption such as that provided by Enigma a user of Burn can keep their system's sensitve data completely secure.

Although Next Wave Software reserves all rights to Burn (especially for-profit redistribution), it is a free program provided as a service to the Macintosh community.
Key Features of Burn

* Lightning fast file erasure
* Scriptable
* Erase Free Space command to protect all sectors on your disk
* Easy drag-and-drop interface
* User configerable erase pattern and erase passes

http://www.thenextwave.com/burnHP.html