Transparency International recently released its annual Corruption Perception Index. You can access the full report here and an interactive corruption map here.

The Bottom Five Most Corrupt Countries:

176 (tie). Iraq
176 (tie). Sudan
178. Myanmar
179. Afghanistan
180. Somalia

The Top Five Least Corrupt Countries:

1. New Zealand
2. Denmark
3 (tie). Singapore
3 (tie). Sweden
5. Switzerland

Update: The BBC recently published an extremely interesting article on corruption in Afghanistan. Money quote:

"The Bertelsmann Foundation, one of the sources for the conclusions of Transparency International, said: 'Corruption is endemic to all state functions (police, judiciary) and is seen as a usual form of business transaction; even ministers were involved in land grabs. Corruption is additionally interlinked with the opium business. Thus, bribery is invested on a massive scale to undermine efforts against the drug economy.'"
Read the full article here.