StumbleUpon, although one of the lesser-known social media sites, has a big claim to fame: it drives more traffic to websites than Facebook. Now, before you jump to conclusions and abandon Facebook, take into consideration the nature of StumbleUpon - it is a website referral site. Its whole existence revolves around recommending webpages just for you, so of course it's going to drive a ton of traffic. Nevertheless, don't discount StumbleUpon, it just might be the next big thing in internet marketing. It's definitely one to watch.

In the past 16 months, the personalized discovery engine has doubled its user base. It now has more than 20 million registered users who “stumble” (click a button to load a webpage the site has picked out based on users’ preferences and behavior) more than 1 billion web pages every month.