Here’s another excellent source of information from an NGO, Transparency International, that investigates, writes about, and collects data dealing with corruption. This NGO puts out an annual Transparency Index, listing countries around the world with respect to the level of corruption in each.
What is Transparency International?
Transparency International, the global civil society organisation leading the fight against corruption, brings people together in a powerful worldwide coalition to end the devastating impact of corruption on men, women and children around the world.
TI’s mission is to create change towards a world free of corruption.
Transparency International challenges the inevitability of corruption, and offers hope to its victims. Since its founding in 1993, TI has played a lead role in improving the lives of millions around the world by building momentum for the anti-corruption movement. TI raises awareness and diminishes apathy and tolerance of corruption, and devises and implements practical actions to address it.
Here is a link to the Corruption Perceptions Index (CPI), and Bribe Payers Index (BPI), among others. There is a wealth of information on this site related to corruption.