Youtube is a largest video sharing site on web, with registering millions of videos and views daily.
Here we will see how to find top viewed videos on Youtube across all location of world or for a specific country.

Point your browser to open following link

When the page is loaded in browser you will see the tab selection as below;"Most Viewed" and "All Time", and then followed by list of videos.

One thing you need to verify here is, if you want to see most viewed list across the world you need to select link "Worldwide", by clicking on Country name next to YouTube main logo and select "Worldwide(All)", if its not already selected.

Simillarly, one may also use this tip to find most viewed videos in specific country by selecting any of country name from same pop up as shown above.
Finally you will have a list of videos that are viewed by millions across web along with there view count.

There are even other options available like most viewed for today, week or month. Also most discussed, most favorited, most responded, top rated, recent videos, rising videos, spotlight videos. You can access these options from menu bar similar as below: