You can’t, of course, go past Prison Flicks, even if it’s been a bit quiet lately.
Or if you’ve really stumbled on this site by mistake – and what you were really after was some intelligent, knowledgeable discourse about film of all sorts – you should perhaps give Cinelogue.com a go. There’s even a section on the prison film genre.
There are plenty of noir movie sites. I like Where Danger Lives, particularly for the graphics.