This is my favourite film that Gary Oldman is in but his performance as Agent Stansfield in Leon is too amazing to not have as number one. Having said that his performance as Jim Gordon throughout the Dark Knight Trilogy is the stuff of amazement as well. Not crazy and loud this time, but cool, collected and yet still just as effective.
My favourite of the Harry Potter films with Gary Oldman's Sirius Black becoming my second favourite character (after Luna). I liked the character when he was introduced in Prizoner of Azkaban and thought Oldman gave a perfect performance, however it wasn't until this film that I was really convinced he was a good guy.
He only gets a small role in this, but his characters pretty awesome (his first act is to obliterate a car with his tommy gun!). He looks pretty cool as a depression era gangster, another trait to add to his perfected list..