Prototype of idea: Last.fm TagCloud Shirts
I came up with this idea a year ago (or maybe two), I don't remember.
It is very simple: Last.fm gives you the artist you most listen, and usually teenagers are proud of their taste and want to show what they listen nowadays.
This website would allow to buy a t-shirt with a tagcloud of your bands/musician you most listen, based on your last.fm account.
I also made a little prototype: http://www.patriciotarantino.com.ar/labs/lastfm/
I am pretty sure I am not going to develop, mainly because I don't know anything about t-shirt making proccess, but if anyone wants to refurbish the idea, or use as it is, I would be glad to see it implemented.