I also second “The Lion In Winter”- outstanding film, and Peter O’Toole was robbed (Katherine Hepburn won for “Guess Who’s Coming to Dinner” the previous year, but it was a valedictory award, and I’m not sure people would have voted for her had they known just how outstanding she was going to be the following year in “The Lion in Winter”!).
In addition to what others have listed, try some of the following.
If you like 2— or 3-plus hour sweeping historical epics, see:
“Lawrence of Arabia” [Peter O’Toole as the title character]
“The Last Emperor” [The life of the last Emperor of China- aside from the historical aspects, a great study in solitude at its epitome.]
“Ghandi” [Ben Kingsley shot to stardom with this film, and it’s his best role to date, I think]
“The Great Escape” [WWII POW camp film, featuring, as the title says, an escape. Worth seeing at least once, so you can reference why people talk about Steve McQueen and motorcycles in the same sentence.]
“Das Boot” [Another WWII flick, this one set in a German U-Boat. You’ll never see submarines the same way again. “U-571” is entertaining as well, but I’d go with “Das Boot”.]
If you’re interested in sword-and-sandals movies, you could watch:
“Spartacus” [One of Kirk Douglas’s iconic roles, and Kubrick’s more popular entry in historical epics, compared with “Barry Lyndon”.]
“Ben-Hur” [“This is the day, Judah. It’s between us now.” Even if you find the movie a bit cheesy (Charlton Heston, anyone?), it’s worth watching (and re-watching). A very long movie, and I usually fast-forward through the Overture and Entr’acte to shorten it, but worth watching at least once. One of these days I must watch the 1925 silent version.]
Other historical epics in other time periods/genres that I recommend:
“Empire of the Sun” [this is one of the few underrated Steven Spielberg movies around. While I find something cheesy in most of his movies, no matter how well executed, this one is straightforward and harrowing, without any maudlin moments. It’s the story of a young British boy in WWII China who is interned by the Japanese (a time period and aspect of WWII that isn’t generally portrayed in film/literature, so that’s fascinating in itself), and it’s based on J.G. Ballard’s autobiographical novel (worth a read). Christian Bale is great in this movie.]
“Matewan’ [In this era of inequality and labor struggles, this one is worth watching. John Sayles’ take on 1920’s West Virginia coal miners trying to establish a union in the face of hostile mine owners/management.]
If you like television, you should try these:
“Roots” [good exploration of the black experience in America, over several generations.]
“Lonesome Dove” [Larry McMurtry’s books are outstanding, but they’re also quite cinematic; most of his books have been turned into movies/tv miniseries. This one is about the last hurrah of aging Texas Rangers who commandeer an epic cattle drive from Texas to Montana. Great performances from Robert Duvall, Tommy Lee Jones, Anjelica Huston, Diane Lane, etc.]
“I, Claudius” [based on Robert Graves’ books (must-reads), this is a BBC series about the lives of the first Roman emperors as narrated by Claudius. It’s a soap opera, but well done and gives you some insight into the times]
There’s more I could suggest, but I think this is plenty for now. ;-)