Are we talking at one time or over the period of say a day/week/month?
I know there are a few collage football games in the US that are over 100K at the time of event (Michigan/Ohio games in Michigan)
Comic Con SD and Comic Con NY each have 100K over the course of 4 or 5 days depending on what day you official count it.
Brazilian Carnival is quite large.
Are you looking for viewing, super bowl has lots of views.