I use a number of archive sources on this blog. Here is where they come from:
CAMD RF (ЦАМО РФ): Central Archive of the Ministry of Defense of the Russian Federation. The archive has existed since 1936, and contains over 17 million items. Physically located in Podolsk.
RGVA (РГВА): Russian Government Military Archives. Established in 1920. This archive contains documents pertaining to the history of the Red Army and the MVD/NKVD, as well as foreign documents imported into the USSR. Physically located in Moscow.
RGASPI (РГАСПИ): Russian Government Archive for Socio-Political History. Of the archives used by this blog, it is both the youngest (established in 1999) and has the oldest documents (dating back to 1617). Of course, I don't use materials that old. Physically located in Moscow.
RGAE (РГАЭ): Russian State Archive of Economics. The archive contains economics-related materials from 1917-1994, and individual documents dating back even earlier than that. Physically located in Moscow.