The big daddy in this genre, no other site has got as much publicity as MySpace has. It was started by Tom Andersen and Chris DeWolfe in November 2003 and was acquired by Rupert Murdoch's News Corporation in July 2005 for the value of US $580 Million.
As every social networking sites MySpace can add your pictures, make friends, upload music and videos, chat will your buddies and many more. Writing blog and inbuilt game choose option is an added feature which others has least. The GUI of MySpace offers a complete leeway to modify and customize your profile page. You can choose to change the color of the profile. You are the master of your profile, just you need to do is copy paste simple HTML and CSS code. MySpace profile editor is a good option too.
Whenever you create a new account, Tom Andersen (the founder) gets added to your friends list by default. Since he remains a friend of majority of the users it can be a place to get friends. MySpace has separate areas for film makers, musicians and comedians. You can add music to your profile and join groups you like.
As the site design goes, the user profiles is reported to cause problems from messed up views to browser freezes to music and video . In fact MySpace does not conform to W#C standards of valid HTML usage. Even more to go, MySpace is a haven for phishers and spyware. Safety for underage users also remains a concern.
With a extreme user base about 200 million and available in languages like French, Spanish, German, Chinese, Japanese and of course English, love it or hate it, you cannot escape MySpace.
Facebook was the leader in social networking space until MySpace took that position. Facebook was originally started as social networking website for the college students. Though it is now available for anyone, it remains the most popular site for college students,with +69 million members and about half of them are college students.
Facebook was founded by Mark Zuckerburg in February 2004 from Harvard University. In September 2006 Facebook became accessible to anyone. As in MySpace a user can modify their profile layout but cannot add HTML/CSS or Flash. Hence there in no problem with browsers and the profile loads comparatively faster.
Users can join the network and groups. There are lots of networks of colleges of different countries and can joined according to the country. Groups are places where peoples meet up with their common interests. Facebook allows you to add applications in your profile. Applications are like widgets that do like listing your all friends, list the books you like and many more. To view another profile you need first to be a friend of that member.
There is Facebook badge where you can share your information in other web sites. There is an activity log system which keeps track of everything you do while your stay at the site. Market place is a new feature added where you can conduct business.
With an easy setup/registration, its cool features, Facebook is truly worth a visit for non members.
Orkut is one of the most popular social networking site in places like India, Brazil and US. Orkut was started in January 2004 by Google employee Orkut Buyokkoten, a Turkish engineer. Orkut was launched keeping in mind the US market but it found more popularity in Brazil. The top 3 demographics are Brazil (56%), US (19%) and India(15%) while visits country wise are Brazil (72.5%), India (16.1%) and US (2.7%). The second data is more reliable as you can put any country as their place of birth or residence.
Orkut offers a very friendly and uncluttered interface in the tradition of Google, you don't have the customizable option like the MySpace. The members need to have a Gmail account. Members communicate through scraps (they are used widely in Orkut).
People can get together with groups (community), upload pictures, videos (you too have the Google and youtube videos) and many more. You have inbuilt chat feature same like the Gmail. RSS feed for your blogs as well as Orkut's very own blog open to all users.
With its popularity, it too has controversies. It has been banned in Saudi Arabia and Iran. In Brazil the charges of propagation of racism by users, in India the target of political parties and in the area of security the site is vulnerable to cross scripting attacks, phishing, malware and viruses.
Thats it about the Orkut, with the vulnerabilities Orkut is not getting less popular.
Those were the top 3 i got for you guys and more to go on here.