Social Networking explained:

Social networking services usually allow users to create an online profile for themselves. Users can upload a picture of themselves and can often be "friends" with other users. In most social networking services, both users must confirm that they are friends before they are linked.

For example, if Alice lists Bob as a friend, then Bob would have to approve Alice's friend request before they are listed as friends. Some social networking sites have a "favorites" feature that do not need approval from the other user. Social networks usually have privacy controls that allows the user to choose who can view their profile or contact them, etc.

Some major social networks have additional features, such as the ability to create groups that share common interests or affiliations, upload videos, and hold discussions in forums.

Bebo

Bebo is the next generation social networking site where members can stay in touch with their College friends, connect with friends, share photos, discover new interests and just hang out. (taken from the Bebo website)

Bebo is the 86th most popular English-language website

Myspace

Create a private community on MySpace and you can share photos, journals and interests with your growing network of mutual friends!(taken from the Myspace site)

Facebook

Facebook is a social utility that connects people with friends and others who work, study and live around them. People use Facebook to keep up with friends, upload an unlimited number of photos, share links and videos, and learn more about the people they meet.

Bebo

MySpace

Facebook

List of other Social Networking sites (including blogs)