For October, I've picked Fritz Lang's 1945 film noir Scarlet Street. As I said in the other thread, I believe this is one of the greatest film noirs, and I love the way it blends many the traditional elements of noir: tons of shadows, bland everyman protagonist, femme fatale, heavy dose of cynicism, a far fetched plot with many juicy twists, and frequently shifting sympathies.
Here's Ebert's guide as to what comprises a film noir, which could come in handy.
And this chart is good to link too.
I'm looking forward to discussing it, and re-watching it this week. I'll post more thoughts then.
The whole film is available on YouTube. It's not the greatest quality, but it's also streaming on Hulu, and DVDs are fairly easy to come by.