21. Melora Walters
Walters played a beautiful, somewhat airheaded porn star in Boogie Nights, but her best part came as the promiscuous, emotionally wounded junkie Claudia Gator in Magnolia. You'd think that such a broken character would be mired in pathos, but Walters gives a surprisingly tough performance here: Her self-loathing manifests as aggressiveness rather than mopeyness. It's a smart choice, and helps make the character — who, in her broad strokes, could have become nothing but a cliché — far more interesting.