I just had a chance to read "The Bottom Billion", a book by by Oxford University economist Paul Collier. He used to work for the World Bank and for the British Government and has created a model for why poor countries remain poor and then describes steps on what "Top of the Pyramid" countries can do about it. It is compelling reading, especially the prescription part.
His model is based on four "traps" that countries fall into that prevent them from growing: Conflict, Natural Resources (too many of them), Landlocked with Bad Neighbors, and Bad Governance. According to his research, 58 countries with a combined population of 980 million fall into one of these categories.
The book has a lot of interesting facts about the traps, for example, the "typical" civil war in Africa costs a country $60 billion in economic growth. He then goes on to assert that trade and aid policy from developed countries should be tuned to the specific trap a country is in. What works for a country emerging from a civil war will not necessarily work for a country with poor access to ocean ports.