I like a good Grindhouse horror movie, but I particularly enjoy movies that are very sensational, something that assaults your senses. Like Requiem For A Dream, or a David Lynch movie (obviously not Dune or anything like that, stuff like Eraserhead). This can be any genre really, but I find that it mostly falls into the thriller/drama genre.

Also, a dumb, explosive action flick every now and then is good for switching your brain off for a bit.

I think horror just might be my favourite though.