You like playing FarmVille, but are really not too keen on the idea of paying real money for virtual products, otherwise known as in-game purchases. It’s reasonable to balk at that, but Zynga, the makers of FarmVille, have announced another option for you to earn Farm Cash to make those crop or cow purchases without having to directly fork over your cold, hard cash: just buy real-world items.

Zynga announced today that it’s partnering with American Express to launch the Zynga Serve Rewards Program, a prepaid card program that will give you a Farm Cash kickback with purchases over $25 or more. For those unfamiliar with the service, Serve is a digital wallet where you can transfer and receive funds that’s provided by American Express.

It works like this: you register for the Serve Rewards program in order to receive the prepaid card in the mail. Add money to the card via your real credit card, bank card, or cash (you have to use a GreenDot MoneyPak for that last option). Activate the card and then set out to the mall or boutique or wherever American Express is accepted, make some purchases, and then you’ll receive the in-game rewards in real time.

Dan Schulman, President of Enterprise Growth, American Express, said he’s thrilled to be a Zynga partner. “As the commerce landscape continues to change, and online and offline spending converges, Serve is focused on partnering with companies like Zynga to create unique value for our customers in the environments they love,” he said in a statement.

This isn’t the first partnership that Zynga’s entered with a credit card company to provide benefits to fans of its games. In December, Zynga partnered with Discover Card to launch an in-game rewards program that allowed players to trade in rewards points for a Zynga gift card.

Zynga expects to launch a similar rewards program for additional games later this year, such as CastleVille and CityVille.

Humph. I guess us avid players of Words With Friends just get to keep on keeping on without any fun in-game rewards. That’s fine, Zynga. I don’t need those bonus features anyways to continue to kick everybody’s ass at that game.