ILM chose Arnold as its primary renderer for the jaegers and kaijus in Pacific Rim. In this excellent article, Ian Failes talked to ILM about the challenges of creating giant monsters and robots for Guillermo del Toro’s summer blockbuster. Read more in fxguide’s article, Monster Mayhem: Pacific Rim.
Rodeo FX also relied on Arnold for Pacific Rim. In this article on Art of VFX, Sebastien Moreau, Matthew Rouleau and Fabrice Vienne talk about how they were involved in the film. Below is a breakdown video from Rodeo FX of their work in Pacific Rim.
There are plenty more details in ILM's youtube channel on the overall VFX pipeline, how the jaegers and kaijus were built, and how the incredible Hong Kong night time battle sequence was created: