DC’s late '80s run of The Question, written by Denny O’Neil–lots of noir elements and atmosphere.
Greyshirt from Tomorrow Stories has that feel to it.
Elseworld stories are good too -
Batman : The Doom That Came to Gotham is pretty good, but if you are using Hellboy as a source it’s basically Mike Mignola stealing his own material there.
Another Batman elseworlds too, Batman : Nine Lives which I thought was really cool.
All pretty different time periods though.