The History Place
The History Place: The Nazi Soviet Pact
This site from The History Place provides a photo and caption of the signing of the Nazi-Soviet Nonaggression Pact. Includes a text copy of the agreement, with links to additional information.
Other
The Road Towards the Hitler Stalin Pact and Its Consequences
Essay describing the events surrounding the formation of the German-Soviet Nonaggression Pact in 1939. From a non-English site, but this particular page is English-only.