Courtesy of The Top Ten of Everything, here are the top 10 films in terms of box office for the last 9 decades.

1920s
: The Big Parade (1925)
: The Four Horsemen of the Apocalypse (1921)
: Ben-Hur (1926)
: The Ten Commandments (1923)
: What Price Glory? (1926)
: The Covered Wagon (1923)
: Way Down East (1921)
: The Singing Fool (1928)
: Wings (1927)
: The Gold Rush (1925)

1930s
: Gone with the Wind (1939)
: Snow White and the Seven Dwarfs (1937)
: The Wizard of Oz (1939)
: Frankenstein (1931)
: King Kong (1933)
: San Francisco (1936)
: Hell's Angels (1930)
: Lost Horizon (1937)
: Mr. Smith Goes to Washington (1939)
: Maytime (1937)

1940s
: Bambi (1942)
: Pinocchio (1940)
: Fantasia (1940)
: Song of the South (1946)
: Mom and Dad (1944)
: Samson and Delilah (1949)
: The Best Years of Our Lives (1946)
: The Bells of St. Mary's (1945)
: Duel in the Sun (1946)
: This is the Army (1943)

1950s
: Lady and the Tramp (1955)
: Peter Pan (1953)
: Cinderella (1950)
: The Ten Commandments (1956)
: Ben-Hur (1959)
: Sleeping Beauty (1959)
: Around the World in 80 Days (1956)
: This is Cinerama (1952)
: South Pacific (1958)
: The Robe (1953)

1960s
: 101 Dalmations (1961)
: The Jungle Book (1967)
: The Sound of Music (1965)
: Thunderball (1965)
: Goldfinger (1964)
: Doctor Zhivago (1965)
: You Only Live Twice (1967)
: The Graduate (1968)
: Butch Cassidy and the Sundance Kid (1969)
: Mary Poppins (1964)

1970s
: Star Wars (1977)
: Jaws (1975)
: Grease (1978)
: Close Encounters of the Third Kind (1977)
: The Exorcist (1973)
: Superman (1978)
: Saturday Night Fever (1977)
: Jaws 2 (1978)
: Moonraker (1979)
: The Spy Who Loved Me (1977)

1980s
: E.T. The Extra-Terrestrial (1982)
: Return of the Jedi (1983)
: The Empire Strikes Back (1980)
: Indiana Jones and the Last Crusade (1989)
: Rain Man (1988)
: Raiders of the Lost Ark (1981)
: Batman (1989)
: Back to the Future (1985)
: Who Framed Roger Rabbit (1988)
: Top Gun (1986)

1990s
: Titanic (1997)
: Star Wars: Episode 1 - The Phantom Menace (1999)
: Jurassic Park (1993)
: Independence Day (1996)
: The Lion King (1994)
: Forrest Gump (1994)
: The Sixth Sense (1999)
: The Lost World: Jurrasic Park (1997)
: Men in Black (1997)
: Armageddon (1998)

2000s (As of late 2004)
: The Lord of the Rings: The Return of the King (2003)
: Harry Potter and the Sorcerer's Stone (2001)
: The Lord of the Rings: The Two Towers (2002)
: Harry Potter and the Chamber of Secrets (2002)
: The Lord of the Rings: The Fellowship of the Ring (2001)
: Finding Nemo (2003)
: Spider-Man (2002)
: The Matrix Reloaded (2003)
: Pirates of the Caribbean: Curse of the Black Pearl (2003)
: Star Wars: Episode II - Attack of the Clones (2002)

Source: The Top Ten of Everything