First from T-Men (1947):
Here's a scene from Raw Deal (1948):
They also did He Walked By Night (1948), Border Incident (1949) and Devil's Doorway (1950) together, bit I couldn't find any good clips from those films. Mann didn't get any screen credit for He Walked By Night but he directed most of it, and Alton's cinematography is at its finest, especially towards the sewer sequence in the end, which in all likelihood influenced Carol Reed and Robert Krasker when they made The Third Man (1949). Devil's Doorway is an example of Mann's move away from the city to the western frontier (he did three westerns in 1950), and Border Incident is probably Mann's finest film from the 1940s, but that is a blog post for a later day.