While it is most commonly generalized that Godzilla and Godzilla Raids Again both have an aspect ratio of 1.33:1, the Heisei movies have aspect ratioes of 1.85:1, and all of the other movies in the Godzilla series have aspect ratioes of 2.35:1, it's a little-known fact that these are most often just approximations. The actual aspect ratioes for the films are never drastically different from the approximations, but you'd be surprised to find just how many are wider or less wide than they're commonly made out to be.
Thanks to Animation Shop 3, which enables you to resize an uncropped R2 DVD screen cap from proportiately to 100 pixel height, and thanks to my constant need to find any excuse to stay awake into the night before I go to bed, I present you with the actual aspect ratioes for all 28 Godzilla movies:
Godzilla - 1.33:1
Godzilla Raids Again - 1.31:1
King Kong vs. Godzilla - 2.33:1
Mothra vs. Godzilla - 2.44:1
Ghidorah The Three-Headed Monster - 2.51:1
Godzilla vs. Monster Zero - 2.45:1
Godzilla vs. the Sea Monster - 2.51:1
Son of Godzilla - 2.44:1
Destroy All Monsters - 2.52:1
Godzilla's Revenge - 2.50:1
Godzilla vs. Hedorah - 2.49:1
Godzilla vs. Gigan - 2.49:1
Godzilla vs. Megalon - 2.47:1
Godzilla vs. Mechagodzilla - 2.56:1
Terror of Mechagodzilla - 2.57:1
The Return of Godzilla - 1.75:1
Godzilla vs. Biollante - 1.77:1
Godzilla vs. King Ghidorah - 1.77:1
Godzilla vs. Mothra - 1.77:1
Godzilla vs. Mechagodzilla II - 1.78:1
Godzilla vs. Spacegodzilla - I don't have access to a screen cap of this R2 right now. I'll take one tomorrow.
Godzilla vs. Destroyer - 1.77:1
Godzilla 2000 - 2.26:1
Godzilla vs. Megaguirus - 2.29:1
Godzilla, Mothra, and King Ghidorah - 2.36:1
Godzilla x Mechagodzilla - 2.36:1
Godzilla: Tokyo SOS - 2.36:1
Godzilla: Final Wars - 2.35:1
Also bear in mind that the decimal places in the first numbers of these aspect ratioes are rounded to the nearest hundredth. The aspect ratio of Godzilla: Tokyo SOS, for example, is actually about 2.3639:1 if you draw it out, and the decimal space could keep going out to the most minute little detail. Putting it at 2.36:1 is just rounding to the nearest two decimal places, and that's how it is for all of them. So basically, these stats here are the closest accurate #.##:# aspect ratioes for these movies as can be.
Now if you'll excuse me, John Carpenter's masterful They Live is beckoning me.