12 Angry Men
I think this movie was made for me! I am a sucker for courtroom dramas and this is the best one I have ever seen. It takes place entirely in real time and in one room. Twelve men discuss a capital murder case trying to decide on a young man's guilt.
This is a perfectly crafted script. Within the confines of discussing the case we get a good idea who these 12 men are and where they are coming from. They bring their own baggage with them into the jury room and it clouds their judgment. The film is both a testament to the power of the jury system and a cautionary tale about its inherent flaws.
I was not going to bother changing my top 100 list but I have seen too many films in the last month that have to on the list.