Internet History Sourcebooks Project
Fordham University: Modern History Sourcebook: On American Intervention in Korea, 1950
The Modern History Sourcebook offers a very interesting primary source that presents the Soviet position of the beginning of the Korean War. A great resource for comparing US/USSR claims about the origins of the Korean War.
Other
The Origins of the Korean War: From the Soviet Archives
Three conclusions brought on by newly unclassified documents from the Soviet archives. Offers new interpretations on the beginning of the Korean War, including Stalin's opposition to war.