I think fossen would be the guy for that, from reading
his blog he seems like a lot of the non-mainstream, non-"superhero" type. I prefer the superhero comic, but cop stories are interesting to me too. I really liked the Gotham Central line. It recently ended but they are putting them out in trades. It's basically a story about the Gotham police force doing their job without need Batman's help. It was written by Greg Rucka and really good.
The only real non-mainstream I read are Wildstorm stuff, and that is still pretty much recongized, just not many people read it.
The ones I mentioned earlier are all part of the Wildstorm Universe (which is owned by DC anyways), but they all originated out of the Image comics universe in the mid-90's.