Yahoo

David Filo and Jerry Yang, where the two founders of yahoo and it first started off as a hobby in 1994, they made the site so they can keep track of their interests on the internet but it became something much bigger. Yahoo.com is great website visited by millions each day for many different purposes including: To read the news, to check their emails, to check the weather, to play games and many more
Google

Just like yahoo google.com was also found by two people Larry Page (24 year old) and Sergey Brin (23year old) in 1995 today google.com is one of the best search engine ever in the world
Its not only a search it also has a great language tool.
Youtube

It was three friends Mr. Hurley, Mr. Chen and Mr. Karim. Mr. Hurley worked for Paypal and actually was the designer of their logo so obviously he took the role of being the designer the other two were the code writers. First in 14th February 2005 they wanted a way of being able to share each others video and a few days in Mr. Chens garage came up with youtube the first video was posted on the 23rd of April 2005 youtube started of very slow but thing got bigger and bigger and more and more people signed up it was sold for $1.65 billion to google on November 13th 2006
Live

This great site was launched in 1996 and acquired by Microsoft in 1997 it has over 280 million users and available in 35 languages including Arabic, Bulgarian, Chinese (Simplified and Traditional), Croatian, Czech, Danish, Dutch, English, Estonian, Finnish, French, German, Greek, Hebrew, Hungarian, Italian, Japanese, Korean, Latvian, Lithuanian, Norwegian, Polish, Portuguese (also Brazilian Portuguese), Romanian, Russian, Serbian, Slovak, Slovenian, Spanish, Swedish, Thai, Turkish and Ukrainian the current version was launched in November 1, 2005.
Msn

This site was also launched by Microsoft on august 24th 1996 it is the 5th most visited site on the internet and most of Microsoft services we offered throught this site such as msn messenger.
Myspace

It has over 180 million member profiles and one of the most popular site on the internet used by people to socialize they can upload there picture change the music on there profile and many more exciting features.
Facebook

Facebook.com is a great site for socializing launched on the 4th of February 2004 and founded by Mark Zuckerberg who was a student at Harvard University. At first it was restricted to students of Harvard College but was later expanded to more places.
On average 250,000 new users register per day and the page is viewed over 65 billion times each month
Hi5

Hi5 is another great socializing site which was founded in 2000 by Ramu Yalamanchi. The site had over 98 million members by December 2007. Once users register to the site they create an online profile such as hobbies interests and other information about themselves and they can send and receive friends requests which they can either accept or decline.
Wikipedia

Wikipedia.org is the worlds largest online encyclopedia which was Launched in 2001 by Jimmy Wales and Larry Sanger, it is the largest, fastest-growing and most popular general reference work currently available on the Internet people an upload articles onto the site. Articles are available in 10 main languages
And the sites grow bigger and bigger and by December 2007 Wikipedia had approximately 9.25 million articles in 253 languages, comprising a combined total of over 1.74 billion words for all Wikipedias.
Orkut

This is another socializing which is run by Google it was launched on January 2004 by Google it is similar to Myspace and Facebook this site is the 10th most viewed site on the internet and is available in many languages its is another fast growing site.