Probably the original Karate Kid film - back when I first saw that and had it on VHS I was obsessed and watched it almost daily during an Easter school holiday one year.
Others that have had a fair few repeat viewings are:
Pirates of the Caribbean: The Curse of the Black Pearl (DMC would have had more but this last year has been very busy - along with AWE when it comes out on DVD in November these will have lots of repeat viewings over the years; Sarah, we should all get together for a POTC viewing day, fancy dress and all!).
All the Star Wars films - I watched the 3 prequels at least 4 times each at the cinema!
Kevin and Perry Go Large - it's utterly stupid but in a purile way I find it most amusing.
Dirty Dancing - what guy wouldn't want to be Johnny Castle? He dives a cool car, attracts the ladies, dances like a demon and beats people up!
Clueless - superb modern-day adaptation of Emma with Alicia Silverstone looking stunning and in a career peaking form.