To be honest, there haven't been that many movies about chess. "Searching for Bobby Fischer" is an obvious example, while "Knight Moves" is an abysmal one. If only Milos Forman (Amadeus) would make the Bobby Fischer bio-pic the world is waiting for.
However, based in what is currently out there, my vote for best chess movie ever is the German film "Black and White, like Day and Night". Made for German TV in 1978 it is the story of a mathematician/computer programmer, Thomas Rosemund (played by Bruno Ganz) who develops a chess playing program, only to have it humiliated on live TV by the World Champion. Vowing revenge, he becomes a chess professional himself and tries to become World Champion.
There are a couple of interesting facets to the story. One is the opening that Rosemunds program tries against the World Champion. After 1.e4 e6 2.d4 d5 3.Nd2, the program plays 3. ... a6 and the World Champion, followed by the studio audience, begin to laugh. Of course this is a perfectly respectable line, played by Bronstein amongst others.
The other is that the film makers gave Rosemund every documented psychosis in chess history. From fear of his food being poisoned (Morphy), playing God with pawn and move odds (Steinitz), and paranoid conspiracy theories (Fischer), Rosemund appears to be an amalgam of various mad chess players. But rather than detract from the movie, this made it more interesting.
The only problem is getting to see it. The only time I saw it was in 1983 or 84, when it was shown on SBS television in Australia, and I haven't seen it since. If you are fortunate enough to spot a copy, I do recommend you watching it.