I could not help posting this brilliant map of CPI - or Corruption Perception Index - based on the studies done by Transparency International. I lifted it from Wikipedia, I must admit. The accompanying article on Wikipedia is highly recommended reading too.
Here it is a transparency scale - so, a country scoring 9 out of 10 is transparent, and the one getting 1 out of 10 is corrupt. The colour codes reflect the same - dark green marks world's most transparent countries and the dark red, the most corrupt.