The Spacegodzilla/Destroyer double-feature has both films in widescreen, and while the film quality is pretty speckly (especially on Spacegodzilla) it's watchable, and certainly not something that a kid would likely be bothered by. Both films are dub-only with no Japanese audio option, but if these are for a kid then that shouldn't be a problem.
The Sony DVDs of Godzilla vs. the Sea Monster and Son of Godzilla are the best Big G DVDs on the North American market which you don't already have. Dual-language options and gorgeous-quality prints of the films, just like the Hedorah, Gigan, and Mechagodzilla DVDs that you have. Definitely nab those two. Sony's DVDs of the more recent Godzilla vs. Megaguirus, Godzilla, Mothra, and King Ghidorah: Giant Monsters All-Out Attack, Godzilla Against Mechagodzilla, and Godzilla: Tokyo SOS are also all of good quality, widescreen, and dual-language.
If you feel like exposing your son to more of Toho's Golden Age special effects films, Media Blasters have released several of these films on DVD here in the States. They include:
The Mysterians
Varan
Atragon
Matango
Dogora
Frankenstein vs. Baragon
Latitude Zero
Space Amoeba
Like most of the classic Godzilla movies, all eight of the aforementioned films were directed by Ishiro Honda and featured special effects by Eiji Tsuburaya (sans Space Amoeba, as Tsuburaya had already passed away when they made that one in 1970), so the tone and feel of the films is very much of the same style as the older Godzilla flicks, and they even feature many of the same casts of actors. Varan, Frankenstein vs. Baragon, and Space Amoeba all feature giant monsters prominently, so if that's what your son digs the most then those would probably be your best bet to get him out of these DVDs. But all of these films are fun in and of themselves, so your son would probably like any of them (except maybe Matango; you might need to wait until he's a little older before he could appreciate that character-centric film, as great as it is).
Hope this helps, and hope your son's B-day is a good one for him. How old will he be?


