242 mins. That's the first film I thought of when I read the thread title. I had to watch it for AS English. It really is quite tough to concentrate for that amount of time!
I think technically the longest film ever was a film called The Cure for Insomnia totalling at over 85 hours long (5220 mins). The content of the film is debatable whether to call it a film or not but some people have tagged it as the longest film ever. Trivia from IMDB.com -
http://www.imdb.com/title/tt0284020/ I read somewhere that you can get hold of the tapes somewhere. I think theres over 20 VHS tapes Theme of the film from IMDB.com -
With rock music videos and X-rated footage I want to watch it
1 of the longest films I've seen besides the ones already mentioned like Lord of the Rings, The Godfather and Ben-Hur has got to be Giant coming it at 201 minutes.