Okay, really this should be more of a top 100 list, so these seven are more "off the top of my head" than any kind of definitive selection. There are several kinds of Oscar snubs. There are talented actors, artists and filmmakers who have never been nominated, and others who have been nominated many times and never won. There are great films that received one or two nominations in minor categories (Vertigo, Singin' in the Rain) and great films that received none at all. The ones I've chosen here are the ones that, especially in retrospect, seem like the most obvious omissions.
1. Naomi Watts in Mulholland Drive (2001)
Watts did receive a nomination two years later for 21 Grams, though that was clearly a case of making up for this mistake. In 2001, no one gave a slyer or more canny performance, in any film, in any category. Watts not only plumbed the depths of her soul for material, but also stretched to two opposite extremes of the character's personality, making up the two parts of this great, enigmatic film. It was historically important that Halle Berry won the Oscar that year, but considering the other nominees: Renee Zellweger (Bridget Jones's Diary), Sissy Spacek (In the Bedroom), Judi Dench (Iris) and Nicole Kidman (Moulin Rouge), Watts' snub is a real head-scratcher.