First, the OP’s premise about greedy totalitarian jerks unilaterally attacking “peaceful” countries is an over-simplification. There were no clear-cut imperialists and their victims. There were, generally, some greater and lesser imperialists. Countries with strong and weak military, with good and bad fortunes.
Not only Russia gained. Ukraine1 (under the USSR) also “ended the war with more territory than it started with”, because Transcarpathia wasn’t returned to Czechoslovakia. Republic of China2 obtained Taiwan, which later proved to be an asset critically important for the Chiang’s regime. Ironically, Romania3 “ended the war with more territory than it started with” — it already lost Bessarabia (to the USSR) by 1941, but gained Transylvania from Hungary after switching sides in 1944. Yugoslavia4 also expanded a bit at the expense of Italy and, possibly, Hungary. Allies also permitted Ethiopia5 to de facto annex the Italian colony of Eritrea (although Ethiopia had very little to do with starting the World War II).
1 Arguably had large expansionist aims in 1939.
2 Intermittently clashed with the Empire of Japan over northeast China.
3 Invaded the USSR in 1941 with a force second to the Third Reich’s only.
4 It was NOVJ (the Partisans) who won the war, not the pre-war monarchy. NOVJ certainly aimed to “expand” its presence in the country occupied by the fascists.
5 Had territorial disputes with Italian colonies.