Memorial's database Victims of political terror in the Soviet Union is little by little provided with information collected from Memory Books - from printed ones and from books that have been prepared to be published in different regions of the former Soviet Union. The main content of these books is listings of people who were repressed and a bit of biographical information about them. At this moment Memorial's database contains around three million names, and the collection is knowingly still not complete. The List of the Stalin Executions stands out with its recitation of people who were convicted because of personal sanctions of Joseph Stalin and his closest subsidiaries in the Orgburo (Organizational Bureau), and especially interesting for those whose relatives lived in Moscow during the years of the totalitarian regime might the database MosMemo be, in which people who were arrested or executed are listed according to addresses in Moscow. Or maybe the the database containing 1244 memorials for victims of political repressions on the territory of the former Soviet Union will interest you (some memorials also contain listings of names). 

Since no all-embracing source of information about the victims of the repressions has not been created yet, public libraries with relatively complete collections of Memory Books can be very helpful when looking for information. There is for example the library of the international association Memorial and the Sakharov center in Moscow, and the collections of the Center of Retrieved Names at the Russian national library as well as at the Alexander Solzhenitsyn House of Russia Abroad. The archive of Memorial in Moscow and also some of the regional Memorial-archives contain big archival funds of personal files of repressed persons and collections of memoirs that include a selection of letters, diaries, outlines and articles. When trying to find out what an ancestor had to go through the testimony of a person from the same camp or from the same room might be helpful. Furthermore it is likely that a recollection of your relative is lurking in one of the memoirs.

Lists of persons who were repressed are also presented on the following sites:

The coordinating center in Saint Petersburg's project Retrieved names, the regional sites of Memorial in Ryazan, Irkutsk, Krasnoyarsk and Yaroslavl, the site of the Irkutsk association for victims of the repressions and many more.