i've always wanted to be penpals with some kind of convicted felon.
wouldn't subeta be a good place? lol. i mean you don't write letters but you can communicate bunches through mail and comments and evrything.
Try interpals.net. That's a really good site for international online or snail mail pen pals, as well as language exchange.
If you have an account on Livejournal, there are a lot of communities dedicated to finding penpals. I've personally used this one, and exchanged letters with a couple of different people.