Most slept-on automaker

Definitely Hyundai. Impressive performance and quality, for an unusually low price. Basically, Hyundai is now what Toyota and Honda were in the mid-80s. They've managed to get a loyal following in the US auto market, which is notoriously hard to break into. Especially for economy automakers. (Think Daewoo, Geo, etc.) Plus, their manufacturing plant in Alabama is ranked as one of the best in the nation for quality and reliability. It may take a couple years to overcome the stigma from the early-mid 90's Hyundais being cheap and unreliable, but people are definitely taking notice. The Azera, Sonata, and Santa Fe consistently rate among the best in their class for performance and quality, even against the old favorites the Camry and Accord. I'm impressed...

I think the Hyundai's try to look like the Jaguar's. It seems like they're trying too hard to look classy.

The most slept on? I'm gonna have to go with Audi. They live in the shadow of Bavarian Motor Works and Porche, but their cars offer the same amount (if not better) performance.