Below is a small list mentioning top 5 websites with relevant data
|Website||Unique Visitors||Page Views||Avg time on site|
|870 M||1000 B||25:00|
|YouTube||790 M||100 B||25:00|
|Yahoo||590 M||77 B||11:50|
|Live.com||540 M||78 B||11:50|
|Wikipedia||460 M||5.8 B||7:10|
You can view the full list here
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