With 870 million unique visitors, Facebook is on the top of "The 1000 most-visited sites on the web" list released by Google. YouTube is on second position with 790 million unique visitors. This list has been released by Google Ad Planner. The list orders largest 1000 sites worldwide, based on Unique Visitors (users). This list is updated on monthly basis.

Below is a small list mentioning top 5 websites with relevant data

WebsiteUnique VisitorsPage ViewsAvg time on site
Facebook870 M1000 B25:00
YouTube790 M100 B25:00
Yahoo590 M77 B11:50
Live.com540 M78 B11:50
Wikipedia460 M5.8 B7:10


You can view the full list here
http://www.google.com/adplanner/static/top1000/index.html

This is not surprising that Facebook is on top with a huge pageviews, 10 times greater than YouTube which is at second. Google has not placed its own Gmail ranking in the list, may be for competitive reasons.

After Facebook, Twitter is on the 14 position under 'Email & Messaging' category. Wikipedia is on the top under 'Dictionaries & Encyclopedias'.

Top search engines according to the list

RankingWebsiteUnique Visitors
1Live540 M
2Baidu310 M
3Bing230 M
4Ask190 M
5Soso140 M