Since 2004, Digg.com has allowed users to share and rank blog items, Web videos, and newspaper and magazine articles—in the process becoming one of the top websites in the world. Laden with tech news in particular, Digg draws an estimated 24 million unique visitors a month, according to Compete, a Web traffic tracking service, and founder Kevin Rose has become one of the poster children of Web 2.0. Now Digg's success has spawned a rash of rivals, not to mention competing services from Microsoft (NASDAQ:MSFT), Google (NASDAQ:GOOG), and Yahoo (NASDAQ:YHOO). Here's a look at some of the upstarts.

The brainchild of Huffington Post co-founder Jonah Peretti, Buzzfeed tracks the most popular stuff on the Web. Bloggers love the New York City–based site's bite-size listings, which are heavy on pop culture, quirk, and girls in bikinis. And unlike Digg, which tracks how many users have recommended a link, Buzzfeed tracks actual clicks. Current traffic: One million unique visitors a month

Founded in 2007, Filtrbox targets professionals who want to keep tabs on specific search terms, like a competitor's name. The site is already making money. It charges $20 a month to track 25 topics or more and $100 a month for access to its archives. Filtrbox makes it easy to weed out information you don't want and to track how many times a search term is mentioned each day, so you can see sudden spikes. Current traffic: 1,300 users

Culling suggestions from a network of 11,000 Twitter friends, Guy Kawasaki's Alltop.com provides a digest of the world according to the popular technologist and his cronies. 'Many sites believe in the wisdom of the crowd,' Kawasaki says. 'We don't.' The site updates pages on 70 topics (including gadgets, small business, and China) every 10 minutes. Current traffic: 204,000 unique visitors a month

Barely out of the gate, Social Median marries news with social networking. Users join networks devoted to their interests, city, or career, and each network's members add links to an ever-changing wiki. Founder Jason Goldberg came up with the idea at the gym. He saw 50 people on treadmills blankly watching CNN and reasoned that they must want customized news. Success depends on the site's ability to attract devotees. Current traffic: 2,400 users

The Line: Buzzfeed is fresh and fun and boasts the most traffic. But the bigger the site gets, the more it will bump up against the news aggregation services run by Yahoo and Google, as well as Digg. Meanwhile, by copying the Bloomberg playbook and pursuing paying business users, Filtrbox seems to have staked out a profitable niche for itself.

Correction: The original version of this story, which appeared in the October 2008 issue, understated the Web traffic for Alltop.com. As of July,the site drew 204,000 unique visitors a month, according to Compete, a tracking site.