As far as Godzilla flicks go, I'd say nearly anything prominently featuring Godzilla Jr. is campy shit you should only watch if you're in for some 'so corny it's good' material. Most stuff featuring Mechagodzilla or King Ghidorah is great, though.
Also most '60s/'70s monster movies by Toho and Daiei are great, from what i've seen. Matango and the Yokai Monsters series are also recommended, although they dont exactly feature giant monsters.