MySpace (with 57 million monthly users in the U.S.) and Facebook (with 22 million a month) are by far the largest general-interest social networks. But for companies that market to niches, one of these specialized social networks may be a better venue:

An online Rolodex
Users: 5.4 million per month
Marketing options: You can set up a page for free and send unsolicited messages to potential leads at a cost of $10 per message. Advertising rates range from $45 per thousand impressions for ads that run across the entire site to $75 per thousand if you want to reach a specific group--say, accountants in the agricultural industry.

A network for Latinos
Users: 384,000 per month
Marketing options: Setting up a profile is free, and small advertisers can buy ads through Google AdWords. More involved campaigns, which include banners and full-page ads, range from $10,000 to $500,000.

A social-shopping site for wine lovers
Users: 200,000 per month
Marketing options: When users click to buy a recommended bottle, a wine store will pay Snooth 35 cents for referring the user.

An iTunes--social network hybrid where labels and users stream free music and video
Users: 1.7 million per month
Marketing options: You can create a profile and upload MP3 files for free. Marketing campaigns that include ads and sponsored playlists run from $10,000 to $1 million.

A tony invitation-only network for global jet setters
Users: 160,000 per month
Marketing options: Because the site is closed to the general public, you can't just sign up and ping the rich. Campaigns for luxury advertisers like Johnnie Walker, Armani, and Mercedes-Benz span the entire site and can run more than $100,000, but ASW also runs locally focused advertising campaigns and will organize small custom events, with rates that start at $25,000 a month.

Source: Nielsen Online, November 2007