Free online file conversion service

YouconvertIt lets you upload audio, video, image, or document files and convert from one format to another. Just select the file from your computer to upload, select your target format, and the web service will send you an e-mail when your new file is ready to download.
YouconvertIt doesn't appear to have a file size limit (although that may change), and currently has no advertising (which will definitely change). Oh yeah, and you can convert units like miles, kilometers, inches, and feet.

The service is definitely fast and convenient. But you get a lot more control over your file conversions if you're using desktop software. If you're converting a document from HTML to text, this might not matter so much. But if you're converting a WAV to MP3 or MPEG-2 to MP4, there's no telling what kind of file size/quality you're going to get with these web-based services. If you need to convert a file and you don't happen to have a good desktop program handy, YouconvertIt will do in a pinch. But we wouldn't recomment it if you regularly need to convert/compress multimedia files.

http://www.youconvertit.com