After years (well, only year really) of wanting to see this one I finally succumbed and bought it.
Luis Bunuel's L'age d'or
Upon my first viewing I was a bit disappointed, since I was expecting an hour long version of Un Chien Andalou, but then I let the film simmer for a few hours and watched it again. This second viewing blew me away. The moments of surrealism were more clear and this has to be one of my favourite Bunuel pieces that I've viewed thus far.