Assetize.com

Allows you to buy, sell and park your online accounts.

I read Coke paid some handsome amount of money to get their twitter account. So, there is definitely a business model in this. Think of a social media as an internet over an internet. How domain parking was a big business at one point, your facebook url, and your twitter url will be of equal importance.

Check it out at: http://assetize.com