In 1957, Colombia issued a set and souvenir sheet commemorating the 50th Anniversary of the Colombian Military Academy (Scott #673-74, 674a). While the set is relatively common, only 10,000 of the souvenir sheet were issued, and Scott '12 prices it unused at $20.00 .
The souvenir sheet is somewhat large, and care should be taken to ascertain that it doesn't have creases or bends before purchasing it. It should do well based based upon the growth of Colombia's economy, and the long-term stealth bull market for better Latin American stamps in general.
A nation of 45 million people, Colombia has been plagued by decades of serious internal armed conflict, drug trafficking, corruption, and gross inequities of income, but has nevertheless racked up impressive annual GDP growth averaging 5.5% over the last 5 years. Moreover, until the global financial fiasco cut its GDP growth to 3% in 2009, it had been steadily accelerating, from 2% in 2003 to 8% in 2008. Recently, the government, armed to the teeth by the U.S., has applied a dual policy of combining military pressure with negotiations to cope with the various guerrilla factions within the country. This seems to have worked to some extent, as the number of insurgents has been halved, and the number of homicides and kidnappings drastically reduced. While some argue that the Colombian government is still utterly corrupt, and has violated human rights and supported paramilitary death squads in order to achieve relative peace, it may be that this is par for the course, given the nation's history. The main challenge that the country faces will be that of sharing more of the wealth with the majority of the population so as to develop more of a middle class and political center. Otherwise, it will devolve into an unstable mess.
Those interested in becoming part of an international community of stamp collectors, dealers, and investors are welcome to join the "Stampselectors" group and organization pages at Facebook. These host lively discussions concerning stamp investment and practical aspects of collecting, and are excellent venues for those who wish to buy, sell, or trade stamps.