Covertfiles.com which converts any file you would ever want to use. Sure you can convert files within Google Docs, but this goes way beyond what you would typically find there or with your Microsoft's files and includes video, audio, e-book, images, archiving. Best of all it can serve as a depository as I have used it (for free) for my friend's band and just connect it to their site. You can also upload the files, once converted, to your site - or others including youtube. Here are all the conversions possible.