I was a level designer at Treyarch for a little over 3 years working on Call of Duty games.
World at War was released in November 2008 on PlayStation 3, Xbox 360, Wii and PC.
I moved to Infinity Ward in the middle of WaW development, but was still able to contribute a handful of levels to the game, most of which were changed to varrying degrees before shipping.
As a level designer at Treyarch, I would design levels on paper, build them out for gameplay, detail them out to completion (with the help of a fantastic art team), do lighting, optimization and bug fix for shipping.  
Every level shown is a product of the whole team, with many assets being designed and implemented by other departments such as art, fx, sound, etc.  These are the levels that I worked on to some extent on World at War.

Full playthrough video
This was the first mission of World at War, internally called "Makin". I worked on it from paper design to near detail complete on some areas, and then other areas (the middle of the map) were changed a bit after I left Treyarch.

As a tip of the hat from some of my old co-workers that finished the level up, you can see "Pvt. M. McCord" was MIA in the loading screen.

As an interesting look into the development of a level like this, check out this concept art from my buddy and former co-worker, Tom Szakolczay. It also shows a screenshot of the level in a really early state. These are called paintovers, and they help the designer know what the level could end up looking like, and gives lots of environmental ideas and details.

Makin Atoll Paintover

click on a thumbnail to see a larger image

Full playthrough video

When I think about working on World at War, I think about this level. I worked on this level from paper design to completion of the first revision. After I left Treyarch, some design changes were made to the final event of the map.

This map was the prototype for WaW, showing that co-op was something we could do, as well as many other technical and artistic achievements. It was also what we showed the press at E3 and other marketing events.

One of the greatest Call of Duty easter eggs ever was added to this level after I left, thanks to my buddy and scripter for Little Resistance, Jesse Snyder.

Ray Gun Easter Egg in Little Resistance

click on a thumbnail to see a larger image

Full playthrough video
Burn Em' Out is a grinder. This map was designed to show off the flamethrower so you fight through trenches for the entirety. Try it on Veteran and you're sure to go crazy.

Not much to say, really. It's a short map, and it didn't change really at all after I left Treyarch.

I worked on this map from paper design to beta.

click on a thumbnail to see a larger image

Thanks to the Youtube users who uploaded playthroughs of these levels. If any of them have a problem with me linking their videos, please email me.