Here's a category that's had a front runner since before the film even came out. I think it's the only category this year with an absolute shoe in for the award.

Josh Brolin for Milk
Robert Downey Jr. for Tropic Thunder
Philip Seymour Hoffman for Doubt
Heath Ledger for The Dark Knight
Michael Shannon for Revolutionary Road

Prediction:
Heath Ledger. No explanation necessary.

What Should Win:
How many people would freak out if I didn't say Heath here? I'm not going to, but I'm just curious. Heath should definitely posthumously take this award, though I've said before that I wish I could have known how his performance would have been received if it wasn't for his untimely death. My biggest beef was with who did and didn't get nominated with Heath, and my second viewing of Milk hasn't changed my mind that I wish Franco was up there instead of Brolin.