The following six versions are all I have been able to find in current release, but the play has a long history of production on film, and it would be intriguing to find some of the older versions.
1953, Andrew McCullough: This one I have not yet seen, but it stars Orson Welles as Lear, and Welles' performances are seldom uninteresting.
1971, Peter Brook: This is probably the most stylized and strange of the Lear productions. It's a black-and-white film, played in furs, at a glacial pace; it's directed by one of the most daring (but not invariably successful) directors of the period, Peter Brook. It was Brook who took it upon himself to direct and produce a six-hour miniseries based on the Indian epic the Mahabharata, widely considered (and perhaps correctly) to the be longest epic poem in the world, and perhaps even the longest single work of fiction (though here quantifications fail).
This particular production stars Paul Scofield -- Thomas More in A Man for All Seasons (the 1966 Zinneman production). It's worth seeing -- it's intense, in a rather slow-paced, mind-warping way -- but if you can only see one Lear, choose another.
1974, Edwin Sherin: After many years, this remarkable version of "King Lear" is once more available through the Broadway Theatre Archive. The universality of the Lear story makes irrelevant the fact that James Earl Jones (Lear) is black: his magnificent voice, bearing, and diction bring a gravity to the part that is hard to find in any other production. See it if you can. Its production values are what one might expect from something filmed a generation ago from a live performance, but its performances make it one of the very best.
Also in the production are Rene Auberjonois (whom Star Trek fans may remember as Odo from Star Trek: Deep Space Nine), Raul Julia in the richly complex role of Edmund, and Paul Sorvino as Gloucester.
1982, Jonathan Miller:This is the BBC Shakespeare Plays treatment of Lear, and as such it has fairly limited production values,; but the performances are worth looking at, and sometimes the whole production achieves a level that is considerably greater than the sum of its parts.
The art direction in this version of Lear is a bit peculiar: the play is given in a somber, almost Puritanical, late Elizabethan garb. It is a color production that seems to go out of its way to pretend to be black and white. The camera work dwells so much on very tight closeups that at points the whole seems very claustrophobic. For all that, however, it contains some moments of real energy. Miller's productions were not (I think) of the caliber of some of the earlier entries in the series, but they are interestingly directed.
Michael Hordern was perhaps one of the least appreciated actors of his overall ability. He was often pigeon-holed in comic roles (e.g., A Funny Thing Happened to Me On The Way to the Forum), but his range was much wider, and here he shows something of his range. To the role of Lear he brings a classic sensibility of what the play is about, and how the character can be portrayed without a particular angle or agenda or overlay of any sort. It does not, perhaps, break any remarkable new ground -- but it is very solid.
1984, Michael Elliot: This marks the end of Laurence Olivier's long and distinguished career as a presenter of Shakespeare on film -- and indeed, as an actor altogether. When it was made, Olivier was old and sick, and the Lear is accordingly not the towering picture of physical grandeur reduced to impotence and madness; it's probably the most underplayed of Olivier's roles (with the result that even those who don't like Olivier's scenery-chewing earlier performances might find this one worthwhile).
The cast includes a collection of notable actors: Jeremy Kemp, who seems to have played a Nazi more often than anyone who speaks English, appears here in fine form; the varied John Hurt, who has played characters from the psychotic Caligula in I, Claudius, and Master Richard Rich in A Man for All Seasons to the inscrutable industrial mogul in Contact, here takes a turn as the beloved Fool, who speaks (of course) nothing but wisdom throughout. Leo McKern, known as Cromwell in A Man for All Seasons and the old monk in Ladyhawke, and (most famously) as Rumpole of the Bailey, is here Gloucester. Edward Petherbridge, who played Lord Peter Wimsey in the BBC's second series of Lord Peter dramas (after Ian Carmichael's earlier series), is the King of France, and Diana Rigg (the original Avengers, as well as the 1968 Midsummer Night's Dream) is the evilly conniving Regan.
Altogether, the performance is elegantly assembled, and mixed with a melancholy sense that not only Lear but also Olivier is on his last legs; there's a kind of wistful delicacy about it that seems counter-thematic in King Lear, but it works -- though one ought to see at least one other King Lear to see how different it can be under different circumstances.
1997, Richard Eyre: This one I have not yet seen, but Ian Holm as Lear promises to be very good -- probably higher-energy than most of the others, and an interesting foil to the Olivier. Holm (Sam Mussabini in Chariots of Fire, and Flewellyn in Branagh's Henry V) is an actor of very considerable range.
Related:
Akira Kurosawa, Ran. This is a Japanese version of the Lear story, with sons instead of daughters. It's a magnificent example of a cultural transposition of the fundamental story that works despite the enormous gap implicit. It's a gigantic film, with the kind of gravity one finds in the best western productions. It is not Kurosawa's first attempt to work with Shakespeare: his earlier black and white Throne of Blood (lurid and sensationalistic as the title may sound) is in some ways one of the finest tonal expressions of Macbeth ever made. Of course in both cases, the language of the original is lost: they are in Japanese. But they are both a kind of testimony to the universality of the stories Shakespeare has built.