I found a pretty funny article (and by found I mean religiously read this site) about how some of the best movies of all time almost became the next (insert reference to blockbuster bomb here, i.e. Pluto Nash, The Day The Earth Stood Still, and any Kevin Costner movie after Robin Hood). Well any way I think I used up my parenthesis quota for the day so check out the article.
http://www.cracked.com/article_16940_6-classic-movies-that-narrowly-avoided-disaster.html