Okay, so maybe Frank Darabont's adaptation of Stephen King's horror novella doesn't really fit under the "kaiju" banner, but monsters are monsters, and The Mist boasts a huge collection of otherworldly creatures that come in all shapes and sizes. Big spiders, mini pterodactyls, enormous praying mantises, colossal, indescribable beasts...there's a critter in here for everyone, with a huge emphasis placed on practical FX work over CGI.
But it's the basic conceit of The Mist that really makes it a good aperitif for Pacific Rim. After a lot of talk about dimensional portals, it's clear that the various creepy crawlies attacking the small Maine town in which The Mist is set come from a whole other sphere of existence from our own. They're not man-made; they're natural-born aberrations brought to Earth by a rift in space, just like the interloping kaiju in del Toro's own story.