Viral marketing is all the rage but, as many companies are finding, it's hard to pull off. And even if a campaign draws considerable traffic, that's no guarantee that the marketing message itself reaches the target audience. That said, the folks at Marketing Sherpa have compiled their fourth annual list of the best viral campaigns (here's the link). Among this year's winners:

• Vibe Media's "Vibe Verses" campaign, which invited users to post, share, and rate rap lyrics online. A winner was picked by user vote, and won a prize. The campaign went viral in 36 days and drew tons of traffic to the site, making it profitable. But along the way, Vibe reported there were many efforts to game the vote, which made the campaign harder to organize and administer than they had expected.

• Montreal-based Pazazz's viral video campaign, in which Warren Werbitt, the company's aggressive-sounding president and CEO, delivers an in-your-face, funny, slightly profane rant that lays out why he LOVES being a commercial printer.

The video, according to Marketing Sherpa, helped to establish Werbitt as an industry celebrity of sorts, and drew more than 135,000 views on YouTube. The company has received 800 inbound calls from potential customers that cited the video.

• Playing off the company's signature "Tested Tough" campaign, Columbia Sportwear asked customers to post stories about how Columbia's gear and apparel survived grueling situations. The company offered a prize for the best story. The goal was to generate more traffic to the website and encourage a sense of community, while also reinforcing the brand's positioning in terms of durability. The company had, in the past, asked users to share video or photos of their Columbia products; in this campaign, Columbia decided to make visual content optional, to improve response rates. More than 6,000 customers shared stories, which was a third more traffic than the company had projected at the outset of the campaign.