The Fiscal Reform and Economic Governance Project has just released it latest Collecting Taxes database for 2008/2009. This newest release includes coverage of even more countries and several new indicators. The Collecting Taxes data system features objective measures of revenue performance, tax structure and tax administration across nearly 200 countries.
See: http://www.fiscalreform.net/index.php?option=com_content&task=view&id=759&Itemid=134
(site en English)