http://en.wikipedia.org/wiki/Most_Expensive_Films
According to this, if you adjust for inflation, the most expensive would actually be the Soviet production of War and Peace at about $700mil in today's money.
Known for being one of the longest feature films around (8 hours), and with some outstanding battle scene filming (the Borodino scene featured 120,000 extras, mostly Soviet soldiers dressed in Napoleonic-era uniforms).