The US National Security Archive
Content 
This unique archive covers a vast amount of official and institutional data from US sources mostly little known to the general public, under a multi-level and well-organized format and always up-to-date. Very useful to understand US current affairs.
Selection 
A large and professional editorial board, based at the George Washington University, is in charge of the archive content management
Format
Content material - mostly in a textual format - is available under a well-organized (although complex) structure and many specific areas including a range of declassified documents,
Information density
This unique archive covers a vast amount of unclassified material obtained from various US institutional sources. A very large quantity of information is provided: several hundred thousands records are available to the users (a total of more than 500,000 pages is included in the actual archive)
Content Pertinence to Political Science
With so many data available in an organic and multi-level format, this site is a great resources for anybody involved or interested in US current and political affairs
Updating Rate
The database is constantly updated with new documents, such as Diplomatic Cables, Court findings, "pseudo-secrets" obtained through FOIA and much more