“From Amit Agarwal’s great blog comes another nice online tool. Media Convert is a free online converter service that can convert any audio or video file format into almost any other format such as AVI, MOV, SWF, MPEG, FLV, Real, DivX and several more.
Handles files up to 50MB without any downloads or plug-ins. You can even grab screenshots of any url and more with this tool. Nice page to keep in your list of bookmarks.
UPDATE: Zamzar may be a bit better. Better interface 100MB limit. Check it out.