1. Nauru
This tiny island in the South Pacific may soon be completely uninhabitable, and it's all because the locals forgot to follow the Boy Scout motto: Be prepared. Since the turn of the 20th century, Nauru has been one of the world's prime sources for phosphate, a mineral compound formed over time from bird excrement, and an important ingredient in fertilizer. Phosphate mining quickly made Nauru rich, and at one point, the island even boasted the world's second-highest per capita GDP. But, as it turns out, basing your entire economy on dung can have its drawbacks.
For one thing, phosphate is a limited resource. By 2000, many believed the island's supply had dried up. In fact, all mining ceased until the government managed to hunt down the last few traces of the mineral in 2006. But the phosphate will soon be gone, leaving Nauru without a profitable export and without decent, farmable land. That's because phosphate runs in veins throughout the limestone and coral foundation of the island. To collect it, miners have to rip up the ground, leaving pillars and pits of less-valuable land behind.
About four-fifths of the island is now ravaged to the point that no crops can grow and no one can inhabit it. Worse, the ruined landscape collects heat, which ends up creating a pattern of warm air that prevents rain clouds from forming.
Currently, Nauru imports almost all its food and water, and there don't seem to be any industries poised to replace mining once the phosphate is gone.
EDIT
http://www.cnn.com/2007/LIVING/wayoflife/11/01/mf.see.b4.die/index.html