MySpace is the most popular social networking site, with more than 250 million registered users worldwide. The site is by far the most popular site for the latest in pop culture, with streaming music, videos, calendars and member forums.
Facebook began as a way to connect college students, but after opening the community to the general public it's now one of the fastest growing social networking sites for those over 25. Facebook boasts a community of 150 million registered users and growing.
Twitter is the fastest growing social networking site, and asks users to answer one simple question: "What are you doing?" Answers must be under 140 characters in length and can be sent via mobile texting, instant message, or the web. Users can add a Twitter badge to their Facebook profile, website or blog so that every time they use Twitter (or "tweet," as users call it) it shows up their other sites.
LinkedIn is an "online network of more than 30 million experienced professionals from around the world." By connecting your business contacts with those of your colleagues, you can expand your professional network worldwide. Members use the site to find clients, hire employees, recommend colleagues, and network with other professionals.
Founded in 2005, the site immediately became the premier destination for people to watch and share video with the world, with 71 million unique users a month. Users can also embed video code on their MySpace, Facebook, blogs and websites.
Started in 2005 by two high school friends, MyYearbook quickly became the "hot" place for teens to network. Now more than 2 million teens use the site to play games (and, it appears, buy and sell friends) using cyber money, watch TV shows, and support causes that fight global warming and save rainforests.
With Ning.com, users essentially create their own social network. They define their own profile questions for incoming members, approve members before they join, and enable members to customize their profile pages with their own design, choice of widgets and OpenSocial profile applications. Ning operates much like Facebook or MySpace, but with more flexibility in applications and use.
With more than 70 million registered users, Tagged.com is another site that allows users to create personal profiles, upload video and photos, and chat. The site was designed specifically for teens ages 13 through 19.