The legend of the Yamashita Treasure has been popping up from time to time since the Second World War. As the story goes, when General Tomoyuki Yamashita was ordered to the Philippines for his last stand against General Douglas MacArthur, he also hid billions of dollars worth of gems, jewelry and gold bullion looted from all over Asia. This treasure was purportedly going to be used to build a new army and win the war.
The location of the treasure has varied, from the location of his final stand in the northern Cordillera mountains, to underneath the walled city of Intramuros in Old Manila, to isolated desert islands in the Visayas, and even in Mindanao, a region the Japanese never really conquered.
Several hundred treasure hunters, both local and foreign, have dug all over the archipelago, seeking the lost treasure of General Yamashita. It is said that the Marcos billions came from his discovering the Yamashita treasure during the war.
The contents of the cache are said to consist of mostly gold bars, golden samurai swords, and the like. A common belief is the presence of a huge Golden Buddha statue, weighing several hundred kilograms and worth millions of dollars, reputedly taken from an ancient Burmese temple.
Although dozens have lost their lives in ill-conceived (and ill-equipped) digs, nobody has yet come out with even a piece of the legendary Golden Buddha, or any other part of the treasure. Most skeptics point out that General Yamashita was never really popular in the Imperial Court, and would never have been trusted with hiding such a large sum. Also, no other country has reported missing any large amounts of gold or other precious metals; indeed, the Philippines is a major gold and silver producer itself, and there would be no need to ship these metals into the country, when they could already be found here.
Despite these arguments, there are still many who have devoted their lives to the pursuit of the lost Japanese gold, and numerous local movies whose plots revolve around finding either the Golden Buddha, or the Golden samurai, or even Marcos' famous Golden Arinola (chamberpot).
Chattering_Magpie tells me the Yamashita Treasure is a significant plot point in Neal Stephenson's Cryptonomicon, so the legend may be a bit more widespread outside the Philippines than I originally believed.