Subvert and Submit charge $1 for a Digg vote for your link and claim they can propel whatever they want to the site's front page with their army of 3000+ voters. Does it pay off? They say it does:
"We estimate that we are 50 to 100 times more cost effective than conventional Internet advertising. With Digg, our cost per click is about $0.003, whereas the cost per click of conventional Internet advertising (such as Google AdWords) is about $0.20. Through Subvert and Profit, it costs about $75 to get a story on the front page of Digg, where it will receive about 25,000 clicks. Information about StumbleUpon is less readily available, but our cost per click should be roughly similar. StumbleUpon is a more linear proposition, whereas Digg is all or nothing."
The company also does StumbleUpon.
Also, TechCrunch has a very interesting post about how to get views on YouTube: "The Secret Strategies Behind Many “Viral” Videos".
Digg's Long-Term Effect on Traffic
Dove Spot Hits Digg Front Page
The ROI Of Digg Front Page Spot
Hacking Wisdom of the Crowds
Pay To Get Dugg
Reality Check: Community-Governed News Sites