Good news, Stumblers: Social discovery engine StumbleUpon has completed a $17 million Series B funding round, which will be used to invest in the company’s technology, expand the service to new platforms and hire more employees.

Firms which have invested in the company in this round include DAG Ventures and First Round Capital, along with companies who led the previous Series A funding round in April 2009 — Accel Partners, August Capital and Sherpalo Ventures.

“We are excited to have DAG Ventures join our existing investors in this new round of financing,” said Garrett Camp, CEO and co-founder of StumbleUpon. “With this new investment, we will make it even easier for people to find interesting and relevant content on the Web, whether they are on their desktop, mobile device or even TV.”

Since its Series A funding round, StumbleUpon — which was sold to eBay in 2007 and made independent again in 2009 — has doubled its registered number of users to 14 million and has tripled the number of content recommendations to more that 800 million per month. It launched apps for iPhone and Android in August 2010, and has seen more than 1 million smartphone installs to date. Meanwhile, more than 60,000 markets have used StumbleUpon to promote their products.

I’m a big, big fan of StumbleUpon and I’m delighted with this news as it means the service should be financially secure for several years. I’ve been using the service for years and rarely fail to be entertained, delighted or informed every time I hit that big old “Stumble” button in my toolbar. As per Camp’s comments, I’m fascinated to see how StumbleUpon might work on an Internet-compatible TV.