My fav kaiju:
Other than dear Godzilla, my favourite kaiju is Gezora.
This big weirdo is most well-known as a cuttlefish, but the wonderful thing about him is that he's a Space Amoeba (from the movie Space Amoeba) and he can shapeshift. Obviously the cuttlefish is the superior form, but the fact is that he changes into three major forms during his movie. And that's what rocks.
Another really good one is Daimajin.
He's just a big guy.