According to my.spill.com there are great perfomances that the Academy didn't ever considered. Robert Downey Jr compares in the top 5 list at 3th place as Paul Avery in Zodiac (2007).
David Fincher is one hell of a director, whose credits include The Curious Case of Benjamin Button, Se7en, and Fight Club, and in Zodiac, he crafts maybe one of the decade's best films. This film features a hell of an ensemble cast that includes Jake Gyllenhaal, Mark Ruffalo, Brian Cox, Chloë Sevigny, and Anthony Edwards. However, if there is any standout, it is Robert Downey Jr. as the alcoholic crime reporter Paul Avery. This is probably Downey's best performance between Chaplin and Tropic Thunder. He commands your attention whenever he's onscreen. Also, its Robert Downey Jr., so how can you not get involved with his character?
I would add another great performance of RDJ that deserved an Oscar:
Steve Lopez (The Soloist, 2009)