When Worlds Collide (1951) 82 Minutes. http://uk.imdb.com/Title?0044207#comment
Another planet is found to be rushing towards Earth, but before impact a few people are able to escape on a spaceship via a lottery. Seventy minutes of inept talk followed by a (for its time) spectacular climax. In 50 years time we will laugh at 'Armageddon' and 'Deep Impact' the same way.