I think GT3 does a really good job with this. Look at the parts company at the top of the parts shop. Anyway, here are a couple:
Honda / Mugen
Ford / SVT
Mercedes / AMG
I'm not sure if they're all fully owned. I read somewhere that Mugen was independent but very closely allied/associated with Honda. Seems odd. Maybe that's something more to do with the Japanese kiritsu (sp?) model.