They have alot of this kind of information concerning US, UK and Global Audience Figure Records.
With regards to Series Finales M*A*S*H leads the way by a country mile.
Top 10 are as follows
1) M*A*S*H 105.9 Million 28th Feb 1983
2) Cheers 80.4 Million 20th May 1993
3) Seinfield 76.3 Million 14th May 1998
4) Friends 52.5 Million 6th May 2004 (Only the second highest audience - The One After the Superbowl got higher figures)
5) Magnum PI 50.7 Million 1st May 1988
6) The Tonight Show 50 Million 22nd May 1992
7) The Cosby Show 44.4 Million 30th April 1992
8) All In The Family 40.2 Million 8th April 1979
9) Family Ties 36.6 Million 14th May 1989
10) Home Improvement 35.5 Million 25th May 1999
The list is much longer though and they have lists of most watch TV Events, programmes etc. you find more information here if you are intrested in that stuff.
http://en.wikipedia.org/wiki/List_of_most-watched_television_episodes#Most-watched_series_finales
All the Superbowls of each year are listed with 80/90 Million a time lol.
Just for comparison here are the UK's most watched TV Programmes/Events overall
1) World Cup Final 1966 England v Germany 32.3 Million 30th July 1966
2) Funeral of Princess Diana 32.1 Million 6th September 1997
3 Documentary of the Royal Family 30.69 in 1969 (I don't think people watched much else in those days lol)
4) Eastenders Xmas Special 30.15 Million 25th December 2005
5) Apollo 13 Splash Down 28.6 Million 17th April 1970
6) FA Cup Replay Chelsea V Leeds 28.49 Million 29th April 1970
7) Royal Wedding of Charles & Diana 28.4 Million 29th July 1981
8) Wedding of Princess Anne & Mark Phillips 27.60 Million 14th November 11976
9) Coronation St Xmas Special 26.00 Million 25th December 1987
10) Only Fools & Horses Finale 24.35 Million 29th December 1996
The just outside top 10 in 13th Place was the News Broadcast of the Assissnation of JFK which got 24.15 Million on of course 22nd November 1963.
The UK figures look quite small compared to the US but 32 million for our most watched even is over 50% of the population. Compared to 108m for M*A*S*H in the US which is only arounf 34% of the population. So we don't do too badly.