Angels with Dirty Faces (1938)
It's been awhile since I last watched this one in full, but I just watched the last 20 minutes or so on Turner Classic Movies and was immediately refreshed on just how incredible this film is.
Anyone that considers themselves a fan of gangster flicks - if you haven't seen this already, do so immediately. Cagney gives one of his very best performances, and Bogart shows us his sleazy side in an atypical role.
A truly classic crime drama, deftly directed by Michael Curtiz, who manages to create some great tension throughout. One of the more overlooked classics that more people really should see. The ending alone is one of the most powerful scenes of the 1930's.