I find it rather perplexing that my compatriot chose only Viy out of everything. There are too many to list, but I'll try to mention some of my favs, at least:
Battleship Potemkin is generally recognized as the greatest movie ever screened. Along with Citizen Kane, I guess. Check out why if you are ok with silent era stuff.
Return 2003 one of the most acclaimed movies. A touching story about the father and sons. Might be the best motion picture of XXI, I'd say.
The Cold Summer of 1953 a high-quality action flick.
Thief 1997 a touching criminal drama.
Elder Son 1976 another touching drama about a flippant lie gone too far.
The Irony of Fate 1975 is the most famous movie in my country, probably. It's a solid romantic comedy.
Amour et Pigeons 1985 one more legendary romantic comedy
Burnt by the sun 1994 an eccentric historical drama about the Stalinists era.
Father of a soldier 1965 one of the most touching war movies ever produced.
Autumn marathon 1979 romantic comedy is a popular genre, what can I say?
Palms 1994 I noticed that some ppl enjoy the suffering of others. Kinda both recommend this documentary about leprosy and urge to stay clear as far away as possible as well. The most grotesque and horrific film I've ever seen. People rot in real-time. Their agonizing screams, swarming maggots inside and ineffable torture will sure as hell haunt you for life.
Khrustalyov, My Car! 1998 another historical arthouse if you enjoyed Burnt by the sun.
Cargo 200 2007 a creepy thriller about the serial killer, from the 80s, who happens to be a policeman, too. Nasty stuff galore. Just like in Palms.
Country of the deaf 1998 a decent criminal drama about the deaf mafia
Bury Me Behind the Baseboard 2009 a coming of age drama if you feel like watching something newer.
Ok, I better stop already. Can continue indefinitely, after all.