Zamzar ( www.zamzar.com) is a free online converter that handles document, image, video, and audio conversions in many formats. Simply upload the content (or point to a URL where the content is available for free), select your desired file type, and Zamzar will email you with a link to retrieve the file once it's been converted.

This is a list of file format conversions that Zamzar supports:
http://www.zamzar.com/conversionTypes.php

The file format conversions are in these categories:
Documents
Images
Music
Video

I became aware of this web site by reading the August, 2007, issue of Smart Computing.