I went to visit some family in another state a few years ago. They had "free" PPV and Night At the Roxbury and The Waterboy were on all day, every day. And there was pretty much nothing else on. So I watched each of those at least once a day, everyday, for a month straight.
Other than that experience, though, Fear and Loathing In Las Vegas is probably my top-watched film. I've probably watched it around 25 to 30 times. I watched Natural Born Killers every day for like 2 weeks while I was on the run and my girlfriend was in rehab in another state. I've seen Pulp Fiction and Reservoir Dogs around 15 times each. And when I was a kid I watched the original Star Wars Trilogy constantly.