Spider Monster (蜘蛛怪)
I'm not going to lie to you. This article is an excuse to tell you to watch The Super Inframan.
Sanda (サンダ) & Gaira (ガイラ)
With their humanoid design, Gaira and Sanda are unique in the world of kaijū cinema. They have distinct personalities, making them far more interesting than your average destructive force of nature.
Manda (マンダ)
The concept of Manda is cool, and there's no other monster in the Toho line-up like him, but to successfully pull off a snake-like dragon is obviously a difficult task, which perhaps explains his lacklustre appearances.
Battra (バトラ Batora)
Few monsters follow any sort of path of redemption in Godzilla movies, so Battra's story really does stand out. It's too bad Mothra, being the moth she is, hogs all the limelight.
Gezora (ゲゾラ)
Gezora's design is complex, but he is very simple to describe. He is, quite literally, a giant cuttlefish.
M.O.G.U.E.R.A. (モゲラ Mogera)
Though he's certainly no Mechagodzilla, I quite like Mogera. He poses little threat with his shrewish face and lumbering movements, but his design is impressive and refreshingly bizarre in both his iterations.
Maguma (マグマ)
Maguma is possibly the most gratuitous monster in kaijū cinema history. He was so gratuitous that he didn't even make the cut of the American re-edit of Gorath.
Rodan (ラドン Radon)
I've got quite the soft spot for Rodan. Invasion of the Astro Monster the first Godzilla sequel I ever watched and helped spawn my obsession with kaijū cinema.
Agon (アゴン)
Agon doesn't make the best first impression, but, as he receives more screen time, the execution of the monster costume becomes more impressive, especially for a production company without Toho's money.
Ultralady + generic kaijū + porn = thanks, Japan
Thanks, Red Lady. Thanks, Ultraman. And thanks, Japan. Thanks.