1-Google +
2. Facebook
3. Twitter
4. LinkedIn
5. Wikipedia
6. Digg
7. YouTube
8. StumbleUpon
9. Reddit
10. Yelp
11. Del.icio.us
12. deviantART
13. Yahoo! Buzz
14. Hacker News
15. Newsvine
16. Technorati

Well said this all is good website in social networking.
Also include friendfeed and myspace in this list.

You can get many sites by searching on net, if you want list of top social networking sites you can visit below site: http://www.ebizmba.com/articles/social-networking-websites, http://www.squidoo.com/top-15-most-popular-social-networking-sites-february-2012

Facebook and twitter are most widely used social networking site.

My favourite social networking site is facebook .

Facebook and twitter are most widely used social networking site.

Facebook, Pinterest and Twitter are the most widely used social media website to gain traffic.

They all are awesome, but comparably, I would like to go with Facebook and Twitter. They are outstanding options among them.