Give people some webspace on the server where they can upload various types of files. Then they can upload things and link to them, e.g. flash games, home made mp3 files of music / voice messages, txt docs, whatever.
Allow folk to upload to their own little space and then link to it for others. Give it to people after a certain time / number of posts, whatever.
I know you do this with avatars and sigs, I assume it can be done for other types of file as well. If people can also "manage" their own space by adding and deleting so much the better.
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