I owe you a response here, and I'll do more, but here's the 30s, which is easier, since I know it the least of the three. I'll also stick to Hollywood film, since it seems to suit the question. And since I guess I'll make some rules to myself, to allow myself to stretch them, I'm allowing myself as many as three period pictures* and one non-star picture^ in each set of ten. Period pictures reflect, sometimes more strongly, what an era cares about, while the other exemption allows a worthy other to be included.
1930s:
The Public Enemy (William Wellman, 1931)
-Exemplary pre-Code gangster picture w/ James Cagney & Jean Harlow
I Was a Fugitive From a Chain Gang (Mervyn LeRoy, 1931)
-Socially conscious prison picture w/ Paul Muni
Dinner at Eight (George Cukor, 1933)
-All-star ensemble comedy/drama w/ Lionel Barrymore, John Barrymore, Marie Dressler, Wallace Beery, and Jean Harlow
Duck Soup (Leo McCarey, 1933)
-Anarchic, satiric comedy w/ the Marx Brothers & Margaret Dumont
It Happened One Night (Frank Capra, 1934)
-Populist screwball comedy w/ Clark Gable & Claudette Colbert
Make Way for Tomorrow (Leo McCarey, 1935)^
-Sweet, sad, Depression comedic romance about aging, w/ Beulah Bondi, Victor Moore, and Thomas Mitchell
Swing Time (George Stevens, 1936)
-Light New York musical w/ Fred Astaire & Ginger Rogers
The Adventures of Robin Hood (Michael Curtiz, 1938)*
-Swashbuckling adventure w/ Errol Flynn, Olivia de Havilland, Claude Rains, and Basil Rathbone
Gone with the Wind (Victor Fleming, 1939)*
-Iconic Civil War epic w/ Vivian Leigh, Clark Gable, Thomas Mitchell, & Hattie McDaniel
Young Mr. Lincoln (John Ford, 1939)*
-Unconventional, slow-moving biopic w/ Henry Fonda
1940s:
The Grapes of Wrath (John Ford, 1940)
-Realist Depression adaptation of the novel w/ Henry Fonda, Jane Darwell, & John Carradine
The Shop Around the Corner (Ernst Lubitsch, 1940)
-Light, evocative romantic comedy w/ James Stewart, Margaret Sullavan, & Frank Morgan
His Girl Friday (Howard Hawks, 1940)
-Fast-paced screwball comedy (contrast w/ above) w/ Cary Grant & Rosalind Russell
Sullivan's Travels (Preston Sturges, 1941)
-Serious, satirical comedy w/ Joel McCrea & Veronica Lake
Casablanca (Michael Curtiz, 1942)
-Hollywood-style war romance w/ Humphrey Bogart, Ingrid Bergman, Claude Rains, Sydney Greenstreet, & Peter Lorre
Meet Me in St. Louis (Vincente Minnelli, 1944)*
-Musical heralding onset of post-war darkness w/ Judy Garland & Margaret O'Brien
Double Indemnity (Billy Wilder, 1944)
-Quintessential, sharp noir w/ Fred MacMurray, Barbara Stanwyck, & Edward G. Robinson
The Best Years of Our Lives (William Wyler, 1946)
-Great post-war story of returning veterans w/ Fredric March, Myrna Loy, Dana Andrews, Teresa Wright, & Harold Russell
Treasure of the Sierra Madre (John Huston, 1948)
-Mexican-set adventure noir w/ Humphrey Bogart & Walter Huston
Fort Apache (John Ford, 1948)*
-Community-oriented cavalry Western w/ Henry Fonda & John Wayne
1950s:
A Streetcar Named Desire (Elia Kazan, 1951)
-Method acting vs. Hollywood w/ Marlon Brando & Vivian Leigh
Them! (Gordon Douglas, 1954)^
-Atomic age anxieties fought by science w/ James Whitmore & giant ants
It's Always Fair Weather (Stanley Donen & Gene Kelly, 1955)
-Unconventionally bitter musical seeped in the 50s w/ Gene Kelly, Dan Dailey, & Cyd Charisse
All That Heaven Allows (Douglas Sirk, 1955)
-Adult melodrama of alienation w/ Jane Wyman & Rock Hudson
Rebel Without a Cause (Nicholas Ray, 1955)
-Teen melodrama of alienation w/ James Dean, Natalie Wood, & Sal Mineo
Around the World in 80 Days (Michael Todd, 1956)*
-Lengthy, cameo-filled widescreen epic w/ David Niven & Cantinflas
The Searchers (John Ford, 1956)*
-Racism-themed Western shows shift in use of stars w/ John Wayne & Jeffrey Hunter
Rio Bravo (Howard Hawks, 1959)*
-Methodical, hang-out Western w/ John Wayne, Dean Martin, & Ricky Nelson
North by Northwest (Alfred Hitchcock, 1959)
-Slick thriller of the ad-man age w/ Cary Grant, Eva Marie Saint, & James Mason
Anatomy of a Murder (Otto Preminger, 1959)
-Solid, deliberate courtroom drama w/ James Stewart, Lee Remick, & Ben Gazzara
I'm going to throw the 60s in there too, since it's the last decade of the studio system. And because Stoo's comment makes it seem necessary. This decade in particular can't be understood without the British inclusions; read which films seem to be missing as telling in itself.
1960s:
The Apartment (Billy Wilder, 1960)
-Sad romantic comedy about NYC offices w/ Jack Lemmon, Shirley MacClaine, & Fred MacMurray
Psycho (Alfred Hitchcock, 1960)
-The television aesthetic & non-mystical, non-atomic horror ascend w/ Janet Leigh & Anthony Perkins
The Man Who Shot Liberty Valance (John Ford, 1962)*
-Elegaic Western shoots holes in myth w/ James Stewart & John Wayne
The Nutty Professor (Jerry Lewis, 1963)
-Comedy auteur skewers Rat Pack & college culture w/ Jerry Lewis
Dr. Strangelove: Or, How I Learned to Stop Worrying and Love the Bomb (Stanley Kubrick, 1964)
-Cold War black comedy w/ Peter Sellers, George C. Scott, and Sterling Hayden
Who's Afraid of Virginia Woolf? (Mike Nichols, 1966)
-Explicit language and adult themes in documentary-style drama w/ Elizabeth Taylor & Richard Burton
Guess Who's Coming to Dinner (Stanley Kramer, 1967)
-Socially conscious drama on race is last pairing w/ Katherine Hepburn, Spencer Tracy, & Sidney Poitier
Casino Royale (Ken Hughes, John Huston, Joseph McGrath, Robert Parrish, & Val Guest, 1967)
-The logical conclusion of film excess & a distillation of all 60s pop culture w/ David Niven, Peter Sellers, Orson Welles, Ursula Andress, & Woody Allen
Bonnie and Clyde (Arthur Penn, 1967)*
-American New Wave crime film of youthful rebellion w/ Faye Dunaway & Warren Beatty
The Wild Bunch (Sam Peckinpah, 1969)*
-Violent, men-on-a-mission Western finishes what Liberty Valance started w/ William Holden, Ernest Borgnine & Robert Ryan