I know everyone has pretty much said Metallica. But I'll give you a reason for it. I reckon Andy could turn those useless fuckers into a good band again, make Lars learn to play in time and make Kirk "turn off teh wah" for more than 3 notes and actually play music. I know it will never ever happen, but fuck... I've got a little bit of a chubby thinking about how good that album would sound.
It makes me sad that such an historic event will never happen, but I would go to sleep forever happy if it did.
I love the work that I've heard Andy do, and I'm not a big "omg this producer is amazing" type of person, I just like what I've heard. As long as he keeps working and he's happy, then he's gonna put out kickass stuff. I salute him.