At first, I thought this category had some pretty stiff competition and would be difficult to predict, but as I saw all the films and the awards season wore on, it was made pretty clear who the front runner is here.

Anne Hathaway for Rachel Getting Married
Angelina Jolie for Changeling
Melissa Leo for Frozen River
Meryl Streep for Doubt
Kate Winslet for The Reader

Prediction:
Kate Winslet. Her performance in The Reader is amazing and I'm so glad to see it here. If her other performance this year (Revolutionary Road) had been nominated I don't think she'd have stood a chance.

What Should Win:
Winslet, for sure, though I would have loved to see Hathaway up there as well.