Here's what I found! These are designed for
8-disc DVD cases.

Like I said, I didn't finish the front on Vol. 2, but started it. I was attempting to remake this Destroy All Monsters cover using images of the actual monsters, or replicas of them.

I included the 1998 US Godzilla as the start of the Millennium series since it prompted Toho to make 2000, it is referenced in GMK, and of course Godzilla fights Zilla in Final Wars. I also put the Rebirth of Mothra Trilogy in the Heisei series since it's somewhat related and fills the extra slots.
The front of each features most of the main monsters in that group of films in a collage I made myself. The back lists the movies and their release years, and shows their original posters. The front and back also have "monster icons" for all the monsters. Some of them I had to make myself, since there is no King Kong icon, and the Mechagodzilla icons are the same for all 3 incarnations. I also tracked down the official "Godzilla" and "Godzilla Junior" icons from the 1998 film and altered one to say "Zilla" for Final Wars. The spines match up to create Godzilla's back and spine fins.
I may want to change them some before completing them (which I'm kind of in the mode to do now). Any suggestions are welcome. I'm also considering using a different form of the "Godzilla" logo, since there have been so many over the years. Just search for the real DVD and especially VHS covers to see how many versions there are! This one is similar to one that was on a lot of packaging and toys in the 90s:

If you're really going to be a completest, don't forgot some of the barely-connected films like "War of the Gargantuas" and "Space Amoeba" 
I've considered making a separate collection for all of those related Toho films, including those, Rodan, Varan, Mothra, etc.