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I'm a big fan of classic era noir/detective fiction and films, eg Chandler/Hammett. What comics are there that feature original content in the same style or are adaptations of works by genre authors/directors?

I'm not looking for Sin City knock offs or modern crime stuff, but classic era stories, 1930s-1950s.

You can try the "Noir" OGN from Dark Horse:
http://comicbookdb.com/issue.php?ID=182452

But I don't think it's all set in the 30s - 50s.....

You can also look for Bendis' GN "Torso", it features Elliot Ness going after a serial killer in Cleveland.
http://comicbookdb.com/issue.php?ID=108325

Another would be Max Collins "Road to Perdition" GNs:
http://comicbookdb.com/issue.php?ID=55830
http://comicbookdb.com/issue.php?ID=138292

The BEST examples would be the 2 "Parker" OGNs by Darwyn Cooke
The Hunter: http://comicbookdb.com/issue.php?ID=175028
The Outfit: http://comicbookdb.com/issue.php?ID=212323

Then there are the "Marvel Noir" books which are set back in that time period, but I'm not sure if that's what you're looking for.

Darwyn Cooke's work is outstanding.

I'd also recommend the out-of-print Chandler by Steranko. Look for the trade paperback version, not the mass market paperback size. It's on better paper and you can really enjoy the art more.

A recolored reprint has been scheduled off and on (titled "Red Tide") for years, but no one seems to know when it will be published.

I also thought of the two Road to Perdition books as fitting your requirements (though I prefer Cooke.)

There's a good chance you'll find something to like in The Mammoth Book of Best Crime Comics. It has a lot of my favorite cartoonists: Eisner, Cole, Krigstein (adapting Ed McBain), Raymond, etc. It includes stories by Hammett & Spillane and it's 448 pages.