Hah, funny. I thought of Karnivool before I got to that part of your post. Amazing band, amazing production.
Here's a few names that stand out
(Disclaimer: Production can indeed be a very subjective matter; These are just some subjective favorites)
Band: Heart of a Coward
Album: Severance
Producer: Justin Hill
This is the most crushing modern metal sound I've ever heard, ever. Their heavier moments sound like galaxies colliding. Okay, I'm overselling it, but man do they have a massive sound.
The song "Monstro" stands out the most. I can't listen to it and not imagine some sort of intimidating cosmic phenomenon, be it galactic battles or stars imploding.
-Funfact: They list Karnivool as one of their main influences (though they do have a preeeeetty different sound. But you can hear that progressive element in there.)
------------
Band: Lamb of God
Album: Ashes of the Wake
Producer: Machine
Features what is, in my opinion, the best kick drum in metal, as well as the best produced high tuned metal guitars (I believe most of the album is in Drop D).
-------------
Okay, hope you're sitting down for this one. I might catch a lot of heat for it.
Band: Nickelback
Albums: Dark Horse/Here and Now
Producers: Nickelback, Joey Moi, Robert John "Mutt" Lange, Brian Howes
Lots of people hate Nickelback, and I get why. Personally, I find some of their songs Fun to listen to. Especially on road trips, for some reason.
Their last two albums have some of my favorite "Radio Rock" production. The soundscape is very concert-like. Lots of tastefully used reverb, lots of color. It's an extremely rich sound.
-----------
Band: Nightwish
Album: Dark Passion Play
Producers: Tuomas Holopainen, Tero Kinnunen & Mikko Karmila
This is a bloody masterpiece. There's lots of symphonic metal bands out there, and while I don't necessarily see Nightwish as an epitome of the genre, the way the orchestral and metal elements harmonize on this album is breathtaking.
-----------
Band: Alter Bridge
Album: Fortress
Producer: Michael "Elvis" Baskette
The mixing on this is... imperfect. The snare is a bit harsh on some sound systems. But the soundscapes created in some songs are truly amazing, IMO. There's a certain reverb-y guitar in the prechorus to "Bleed It Dry" that blows my mind every single time.