Check out this interesting report on St. Kitts and Nevis and their experimentation with selling citizenship as a way to increase investment in the country.
http://www.reuters.com/article/2012/02/12/us-passport-idUSTRE81B05A20120212
For decades, the two-island nation of St. Kitts and Nevis exported sugarcane to keep its economy afloat. When sugar prices fell, St. Kitts began to sell an even sweeter commodity: its citizenship.
http://www.reuters.com/article/2012/02/12/us-passport-idUSTRE81B05A20120212