^ Chungking Express is brilliant! I've only watched it once though.

Recently I watched Withnail & I about 3 times in as many weeks. It got better every time. There are a few other films that I'll watch about once a year (A Clockwork Orange, Amelie, Pulp Fiction...) But the real 'movies you never get sick of' that I'll watch pretty much whenever they're on TV / I feel like it are:
Star Trek (2009 - though The Voyage Home is probably my favourite),
The Lord of the Rings (If I catch even five minutes of one I have to watch the whole trilogy)
Love Actually (It comes on TV every Christmas then once in the summer for no particular reason. Still great)
Boondock Saints (This I watched for the first time recently and then watched it the next day and then spent a week watching all the best bits on youtube)