The sale of virtual goods has always been a primary monetization method for social games, and with the world’s most popular sport, soccer, already in the heat of the 2010 World Cup, you can bet that a number of social developers are taking advantage. We’ve already tracked a number of recently-released soccer apps, so below we’re taking a closer look at what non-sports games are doing in recognition of what is, arguably, the world’s largest sporting event.

CrowdStar: Zoo Paradise, Happy Pets, & Happy Aquarium

We’ve taken a keen interest in what CrowdStar is doing for the World Cup, as this particular developer has consciously sought an international image. Taking interest in the soccer tournament makes sense for CrowdStar, as soccer is traditionally more popular abroad than in the United States.

CrowdStar’s most noticeable collection of World Cup virtual goods is in one of its newer titles, Zoo Paradise. Like the majority of games offering related virtual goods, Paradise prominently features flags from the 32 competing countries in the tournament. But flags alone are a bit boring, so CrowdStar got more creative with a second item: a “Soccer Field” habitat for players’ virtual zoos. In order to populate this field, Paradise also offers users three new World Cup animals, including a soccer-playing rhino, a World Cup leopard, and an actual soccer ball animal.

None of these goods can be bought with in-game currency, instead costing anywhere from 10 to 62 Facebook Credits (equivalent to $1 to $6 dollars). Additionally, all of the items are only available until the end of the World Cup series.

CrowdStar has also incorporated limited edition items in two of its other popular apps, Happy Pets and Happy Aquarium. The latter is nothing terribly extravagant, limiting itself to a World Cup stadium and flag backgrounds and an amusing walrus referee. Curiously, however, none of the items explicitly state that they are limited. They still cost either Facebook Credits or the game’s virtual currency, “Pearls,” with the second option requiring marginally more currency.

Happy Pets’ World Cup items, on the other hand, feel a lot more creative in that CrowdStar has provided a way to simultaneously care for virtual pets and support your teams. From French horses, to Italian dogs, to a “World Cup Hamster,” these currently non-limited edition pets take on the color schemes of their homes, and run 88 Facebook Credits apiece. Oh, and for the record, the green hamster rolling about in a glass soccer ball: Awesome.

Zynga: Treasure Isle

While CrowdStar has done a lot, this wouldn’t be a proper roundup without taking a look at Zynga. But, oddly enough, the social gaming behemoth has not contributed as many virtual items as one might expect to the World Cup craze.

Currently Zynga’s third most popular app with just shy of 22 million monthly active users, Treasure Isle, has the most sizable selection of World Cup items, using them to help players decorate their own personal island. Unlike CrowdStar, Zynga is charging its own Cash virtual currency for the special items.

Thus far, the goods consist of animated soccer ball flavor items, some Robinson Crusoe’esque goals, a few flags, and some… “different” soccer playing animals. Beyond a monkey referee, which is pretty cool, Zynga does do something very interesting here; two of the three World Cup animals can be purchased with in-game currency. It’s a hefty chunk of change (11,000 coins), but considering that every other animal in the game, not just special ones, cost virtual currency, it certainly makes for a curious choice. Unlike CrowdStar, the limited purchase time is not until the end of the World Cup, but only a few days from now, so Zynga may be planning a fresh wave of items.

RockYou & Playdom: My Casino & Tiki Resort

On a smaller scale, RockYou! And Playdom have also gotten into the spirit of competition. Beyond mere flags, RockYou! is also selling a virtual rendition of the World Cup trophy within one its newest creations, My Casino. However, in a different approach, the game is not using in-game nor virtual currency for the transactions. Instead, the older company is getting straight to the point through PayPal with items costing anywhere from $0.99 to $5.99.

Playdom, on the other hand, is keeping things simple with a limited stock item for its title Tiki Resort. From within the 5 million MAU strong app, players can purchase a special concession item dubbed “Zulu Concessions” for Facebook Credits. As it stands, there are just over 8300 left.

Foursquare & Bing: Foursqare

While most of these goods have been made available through Facebook games, that does not mean they are limited to the platform. TechCrunch points out that the location-based smartphone game Foursquare is also in the World Cup spirit.

Though they are technically not virtual goods, the game is promoting itself through Bing, offering a World Cup badge for anyone that follows Bing on the service. Additionally, the badge has been tied to any number of sports bars showcasing the World Cup in major cities such as Las Vegas and New York, and can be found via a Bing Map App called HomeTurfFinder on Bing Maps. Moreover, those that follow Bing and check into such locations may also be offered specials there.

In the recent past, we’ve seen virtual goods make up to $1 million a day for occasions like Mother’s Day, as well as Christmas, the Super Bowl, and even Valentine’s Day. If anything, what’s happening around the World Cup is an acceleration of the real and virtual worlds’ convergence — though given the importance of the World Cup everywhere besides the United States, it seems likely that these mostly US-based developers are actually underplaying their hand. On the other hand, there are still four weeks to go for the World Cup, so we may just be seeing the beginning of the marketing push.