Ten months after raising $1 million from Hit Forge, Charles River Ventures, and Bay Partners, Jambool, developers of the Social Gold virtual currency platform for social applications and online games, will announce tomorrow that it has just closed a $5 million Series B round led by Madrona Venture Group. Madrona’s Scott Jacobson led the round and will be joining Jambool’s board.

Since starting out as a developer of social games earlier last year, the company shifted strategy last fall and has been focused on developing its own payments platform and virtual economy tools for social apps and games. Today, the company says it has “hundreds” of publisher partners in social networks and on the web.

The SocialGold platform enables payment with credit cards and bank accounts through PayPal, Amazon, and Google – as well as mobile phone payment in 37 countries through other partners. In addition, SocialGold provides virtual economy dashboards so that developers can learn about payment patterns amongst their users. Which products are most important for the company over the next 12 months?

“All three – payments, currency, and analytics,” says Mike Haswell, VP of Business and Legal Affairs at Jambool. “We will continue to innovate on the payments experience, with deeper and more seamless integrations and, of course, additional payment methods. We’ll build functionality into currency and analytics, both of which are really at version 1.0, over the next 3-6 months.”

However, Jambool says the company isn’t planning on promoting its own virtual currency inside publisher applications.

“We have no plans to offer our own virtual currency,” Haswell says. “We’re focused on enabling developers, publishers, and platforms to launch their own currencies.”

Jambool was founded by Vikas Gupta and Reza Hussein, who led the payments and web services groups at Amazon. The company is part of a burgeoning industry in the US focused on virtual currency monetization and payment solutions optimized for social applications and games. We estimate social network applications alone will do between $300-$500 million in total virtual goods transactions this year.