James Bond - Live and Let Die, I swear the first time I saw it (and most times after) I would go to sleep for hours, and wake up to discover it still wasn't over. I honestly couldn't say what it was about (other then Bond being charming and sleeping with various leading ladies.) A shame as Roger Moore was the second best Bond.
Titanic - A movie about one of the greatest shipping tragedies of all time... only most of the film was absurd ahistorical, flaccid romance with a bit of working class/upper class conflict thrown in. Damn it, if I want something like that I'll watch French art house. Still it was worth it to see DiCaprio die (though like the movie this to took to long)
Any film with DiCaprio - God damn it, why wont it stop! Leave him in the bloody mask/on the bloody beach.
Bad movies in general - Stealth and Doom felt like an eternity.
Movie marathons - Star Wars 1,2 and 3 shown together are even more unejoyable and long then when shown individually (I know this is to be expected.)