Man, there's a whole gaggle of them for me. I won't bore everyone with all of them, but:
A Christmas Story- ever since "It's A Wonderful Life" stopped playing around the clock around Christmastime a few years ago, this movie has been slowly taking its place. I think it comes on something like a hundred times during the month of December, and I catch at least part of it every chance I get.
UHF: Weird Al does weird things at a TV station, with The Nanny and Kramer.
Strange Brew: I usually just call this one "the hoser movie". It was based on some sketches Rick Moranis and Dave Thomas did on SCTV, and involves mice in beer bottles, hockey-player brainwashing, and lots of Canadian pride. Features Mel Blanc!