This site offers a wealth of analytical, theoretical and statistical information on world trade, key players and the position of developing economies. Much of the information is free.  For four decades, "the organization has been the focal point within the United Nations for the integrated treatment of trade and development and related issues in the areas of investment, finance, technology, enterprise development and sustainable development."  

See the extensive set of data/statistics under the Statistics tab, pdf documents within the digital library tab, and more.