Robert J. Randsis . Its a Rat Pack Mystery, really good stuff. There's a few other ones in the series that I'm going to hopefully make my way thru (thank god for library card!). This noir thing just reminds me of a simpler time, the 50's, of course this was just after the war, the real hey day for Hollywood, and before nuclear fears. Not to mention the cars were so friggin bad assed. I mean who hasn't dreamed of having a 50's black caddy? Not to mention all the reading I've been doing, my onstage persona not consists of a dark green fedora (I'm in a rock band called One Blue Door). And as soon as I put it on I'm transported back to that era, you automatically feel more like a gentlemen somehow. All this Noir got me thinking, there must be some Noir based RPG systems out there, so I went ahead and posted it on the Google Plus OSR Forum, and I found a few gems, in case you were thinking of running that type of game.
The next system I found is more of a spy one, but I'm sure you can covert it to be a bit more 50's noir, (which I'm planning on doing) its based on SRD, published by Microlite , here's the link to the pdf http://www2.abillionmonkeys.com:3389/spylite/SpyLite.pdf
A future based Noir game called "technoir" http://technoirrpg.com/index.php
Hoodlums & Hideouts - https://sites.google.com/site/hideoutsandhoodlums/
Mystery Men - http://matt-landofnod.blogspot.co.uk/p/mystery-men.html
Weird Adventures - http://www.rpgnow.com/product_info.php?products_id=97722&src=Blog
Some mini's you can print off - http://www.rpgnow.com/product/24109/Pulp-Set?it=1
And of course I'm sure you can work some Call Of Cthulhu in there somewhere!http://catalog.chaosium.com/index.php?cPath=41
It seems that this idea has already been well thought out! which is awesome. I'm not entirely sure if I will ever run something like this, as it really depends on my players who rooted in fantasy, but its something to think about at this point. In the mean time I'll put my fedora on, grab a scotch neat and open my latest Robert J. Randsis novel, and enjoy.