One of the most interesting things about the TF2 story is that they opened up custom item creation to the community, and allowed players to actually profit from

One of the most interesting things about the TF2 story is that they opened up custom item creation to the community, and allowed players to actually profit from designing and uploading objects to the store. I remember reading a quote from Gabe Newell mentioning that some of the top player sellers were making over $30,000 / month from their creations. edit: If in game, player driven markets are the sort of thing that interests you: keep an eye out for Diablo 3's real money auction house. Also: hats.