In the market for farming supplies?

If you’re looking for a new tractor or some seeds, American Express is hoping that you’ll use one of its new prepaid cards to complete the purchase. On Farmville, of course.

That’s because the company best known for its credit cards targeting businesses and affluent consumers has teamed up with social gaming juggernaut Zynga to launch a new line of co-branded prepaid cards.

The new prepaid cards, which will initially feature Farmville branding, can be funded by an existing bank account, debit card or credit card. As one might expect, holders of the new prepaid cards earn rewards — ‘Farm Cash’ — that can be used to purchase virtual goods in Zynga’s iconic game. The companies say future prepaid cards will target other popular Zynga games, such as Castleville and Cityville.

Interestingly, American Express and Zynga are also using their new prepaid cards as a discount play. According to MarketWatch’s Andrew R. Johnson, “Other companies will have the ability to pitch discounts within the game that players can load to their accounts and redeem by swiping their cards at the participating merchant.”

That naturally raises the specter that Zynga games could start to resemble Second Life, with brands flocking to build a virtual presence in the worlds Zynga creates. Indeed, Johnson notes that another financial services firm, Capital One, last year allowed customers and fans to open their own virtual Capital One branch in Cityville.

Time will tell whether the Zynga co-branded American Express prepaid cards are a hit with consumers, but the deal is a testament to the star power of today’s web and mobile gaming brands. American Express is eager to grow its profile in the prepaid card market, which is an increasingly lucrative and important part of the payments space.

Other players in the space are also turning to digital in an effort to woo consumers, so the fact that one of the most widely recognized financial services names has turned to Zynga in an effort to make itself a more “inclusive brand” speaks volumes about the cultural impact of Zynga’s hit games.