TV movie from the early 80's, "The Long Summer of George Adams" (I think). Starring James Garner as a roundhouse laborer losing his job when the diesels arrive. Set in Oklahoma, but filmed on the Texas State RR. I'd love to see it again, but as far as I can tell it's never been availible on video.
From the 50's: "Night Freight," filmed on location in Modesto, using M&ET 70-tonners and a Tidewater Southern caboose--railroad competeing with evil truckers. Also "It Happened to Jane,"
with Doris Day using a New Haven 2-8-2 to get her lobsters to market. And the British cinematic triumph, "The Titfield Thunderbolt," IMHO the greatest train film ever (and availible through Amazon).
More recently, "The Station Agent," about a railfan dwarf living in an abandoned depot in New Jersey. The scene where they chase a NYS&W train in a snack truck is priceless.