While they aren't available now the folks over at MAKE seem to think that private label MMORPG
credit cards are something that we'll be seeing soon. Much like a Discover card, these cards could potentially allow gamers to earn virtual money when they spend real money as well as offering real world benefits from in-game achievements.
While it's an interesting idea you really have to wonder how much of an uproar these would cause. Given Blizzard's stance against gold farming it's hard to believe they would allow anything like that to occur in World of Warcraft
but for a game like Second Life where there is actually already a mechanism for converting real world currency into virtual currency there may be a lot of potential for such a program to work.
The idea of having real world benefits tied to in game achievements though is a bit out there. While in principle this might sound like a good thing the opportunities for cheating and abuse of bug in the game make this a bit of a pipe dream. You just have to look at the click fraud scandal
that Google is going through right now for an example of a virtual/real world program that doesn't work. I know the analogy is a bit on the specious side but anytime you have a real world benefit that is worth tied to a digital mechanism of gaining it you are going to have people who are going to abuse the system, I don't care how much thought goes into preventing it.