The scary conversion is that you (and your students) can convert PDF files that shouldn't be editable to an editable Word, RTF or HTML document. See a list here.
This site also supports batching up several files to be converted at once.
Zamzar also has the ability to convert videos from sites like Google Video and YouTube.
The interface is super easy to use. First, you upload the file you want converted (or provide the URL), second, you select the format you want to convert it to and then you supply your email address where you will be notified when you can download the converted file. You can't convert files bigger than 100 MB and you have 24 hours to pickup your file.