It was really hard to come up with just 3 films for him so I here is another post with 4 films instead of 3:
The Godfather, Part 2 (1974)
Robert played the younger version of Vito Corleone, who was originally played by Marlon Brando in the 1st Godfather. He won the Academy Award for Best Supporting Actor.
This film also starred Al Pacino, Robert Duvall, Diane Keaton, and Talia Shire.
This film was directed by Martin Scorsese, who also directed Robert in Taxi Driver and Raging Bull. Also starring Ray Liotta, Joe Pesci, Paul Sorvino, and a very young Michael Imperioli, De Niro plays the character Jimmy Conway. This film was based on a true story. De Niro's character was based on a real person named Jimmy Burke.
De Niro plays Sam in this mostly unheard of film that I thought was great. Sam is a former CIA agent who is recruited to a team in Europe to steal (and try to keep away from the wrong hands) a mysterious suitcase.
This film also stars Jean Reno (The Professional, Mission Impossible), Stellan Skarsgard, and Sean Bean.
Men of Honor (2000)
This film, based on a true story, also stars Cuba Gooding Jr. De Niro plays Navy Chief Petty Officer Billy Sunday, who is an instructor for the Navy's diving school. Gooding Jr plays Carl Brashear who becomes the Navy's first black diver.
It also stars Hal Holbrook, Charlize Theron, and Powers Boothe.
Here is a list of major awards that De Niro has won in his career:
Best Supporting Actor, The Godfather Part 2 (1974)
Best Actor, Raging Bull (1980)
(He was also nominated for Best Actor in 1976, 1978, 1990 and 1991).
Golden Globe for Best Actor in a Drama, Raging Bull (1980).
(He was also nominated for Best Actor Golden Globes in 1976, 1978, 1979, 1989, 1991, 2000 and 2002).