Last Days of Planet Earth (1974).

The Scoop:
Giants sea slugs, sentient plants and other assorted beasties threaten to destroy the world -- all in accordance with the predictions of Nostradamus. (As the introductory voice over makes clear, he also predicted World War II, so you know it must be true!) Light on plot and heavy on old guys arguing dubious science, this film also sets a new world record for the use of stock footage. There is supposed to be an environmental activism message here, but that kind of gets lost in the onslaught of cheese. This is strictly bottom-of-the-barrel Toho fare that makes their rubbery Godzilla sagas look like masterpieces. But at least the opening theme music is kinda groovy. And keep an eye out for the scene in which a single car crash pretty much blows up all of Tokyo.

Best Bit:
The well-dressed salaryman sitting in the tree. No reason, really. He's just sitting there.

Side Note:
The original, uncut version of the film is still banned in its native Japan because of a cannibalism scene.

Companion Viewing:
Only a double bill of something like "Godzilla, King of the Monsters" (1954) and "When Worlds Collide" (1951) can give you a hint of what to expect here.

Links:
IMDb.

Take a Look:
Here's the original Japanese-language trailer, which somehow manages to leave out all the coolest, most ridiculous parts (except for the fiery car crash, which you can see a little bit of at the end):